MEMOIRS 
 
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 OK TIIK 
 
 BOSTON SOCIETY OF NATUML IlKTOllY 
 
 VOLUME r,, NUMBER 0. 
 
 THE ANATOMY AND DKVI]f,OPMFNT OT ^ASSIOPEA XAMACHANA. 
 
 liv ;i.)J.LjIT I'AYNK HlGKi.OW. 
 
 BOSTON: 
 
 BY T'.?. socin'ry. 
 
 usT, 1900. 
 
EXCHANGE 
 
 ^It-Cr 
 
 BIOLOGY 
 
 UbRARY 
 
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BIOLOGY 
 
 LIBRARY 
 
 G 
 
 6. THE ANATOMY AND DEVELOPMENT OF CASSIOPEA 
 BY ROBEKT PAYNE BIGELOW. 
 
 INTRODUCTION. 
 
 During the summer of 1891 the Marine Laboratory of the Johns Hopkins University 
 was stationed in the Island of Jamaica. It was at Port Henderson, a little hamlet 
 situated at the west side of the mouth of Kingston Harbor, at the point where the Salt 
 Pond Hill, eight hundred feet high, descends to the salinas and mangrove swamps 
 surrounding the mouth of the Rio Cobre. On the other side of the hill, and to the south 
 of it, there is a considerable body of salt water, known as the Great Salt Pond. It is 
 completely .separated from the sea, but only by a beach of sand, which at its narrowest 
 part is not more than a few rods in width; and it is said by those who live near that in 
 times of storm or freshet this barrier may be broken through. 
 
 One morning in June Dr. G. W. Field was hunting birds along the seaward shore of 
 this pond, and came upon a little bay that forms a deep indentation in the barrier and is 
 connected with the pond by a narrow inlet. The bay is overhung by low cashaw and 
 mangrove trees. At one side is a sunny sandy spot where a crocodile had made its bed, 
 and a fresh zigzag mark showed where it had recently slid into the water. A school of 
 fish was circling about in the clear water, and barnacles and sea-anemones spread their 
 tentacles from the submerged roots of the mangroves, while the bottom at the inner end 
 of the bay was completely carpeted by a colony of beautiful rhizostomatous medusae. 
 
 A few very small specimens might be seen swimming about, but most of the medusae, 
 especially the larger ones, would not ordinarily leave the bottom. They lay there upon 
 their backs, with their voluminous, branching mouth parts spread out over their discs, 
 which were motionless, except for occasional flaps of their margins. If any of these 
 animals were disturbed, they would, however, swim about like ordinary medusae ; but 
 before long they would settle down again and assume their usual attitude upon the bottom. 
 
 1 An earlier draft of this paper was accepted in May, 1892, by the Board of University Studies in the Johns Hopkins 
 University as a thesis for the Degree of Doctor of Philosophy. During the years 1891-92 and 1892-93 I held the Adam T. 
 Bruce Fellowship in the Johns Hopkins University, and was thus enabled to make a second journey to Jamaica. Publication 
 has been delayed in order that the results of this journey might be incorporated in the paper, and it is hoped that the greater 
 accuracy and completeness thus obtained have added materially to its value. 
 
.1.9.2 - . ROBERT PAYNE BIGELOW ON 
 
 Within this limited area there were countless numbers of them, and in many places they 
 were so thickly spread that their margins touched upon all sides, or even overlapped. 
 
 The spectacle presented by this collection of medusae was truly marvelous ; and in 
 order to show something of it to the rest of us, Dr. Field gathered a pailful of specimens 
 and brought them to the laboratory. Upon examination they were all found to belong to 
 a single new species of Cassiopea, a genus of which only one species was known to 
 occur outside of the Red Sea, Indian Ocean, and southwest Pacific ; l and this pailful, 
 taken up at random, contained both adults and young in various stages of growth. 
 
 Professor Brooks made drawings of some of these, and then I made a visit to the 
 Salt Pond to obtain more of the young medusae, and at the same time I collected sub- 
 merged bits of wood and stems of plants. My hopes were more than realized when, upon 
 examining these objects in the laboratory, I found them thickly studded in places with 
 scyphistomas in various stages of development. I was particularly delighted when I 
 noticed in one of the largest larvae certain glistening spots in the bases of the tentacles 
 and found, on putting them under the microscope, that they were unmistakably masses of 
 calcareous bodies that would form part of the marginal sense organs of the adult. They 
 excited my interest, especially as I had been studying the development of these structures 
 in Discomedusae ('90) , and had been unable hitherto to obtain the early stages. 
 
 After this discovery I began, with the advice of Professor Brooks, to make a careful 
 study of this species, with the intention of carrying the investigation of its anatomy and 
 development as far as the limited amount of time at my command would allow. Prelim- 
 inary accounts of my results were published in 1892 (Bigelow, '92, a, b and o) . In the 
 spring of 1893 I had another opportunity to visit Port Henderson with a party from the 
 Johns Hopkins University, and was able to make important additions to my earlier 
 observations. 
 
 During the first visit to Jamaica I was unable to find Cassiopea outside of the one 
 locality that I have described, and, although both the adults and the young in nearly all 
 stages were present at this place in such great numbers, searches for males and for females 
 with ripe eggs were equally fruitless. The great abundance of young and the range in 
 their apparent ages was, therefore, surprising, until I .fou-nd that the scyphistomas were 
 multiplying freely by budding, in a manner to be described later on. During my second 
 visit I found this species as abundant as ever in this locality, and I also found a number of 
 adult specimens in several of the small shallow lagoons among the mangroves in the rear 
 of Port Royal. But these were all females, and it was still impossible to obtain males 
 or eggs that would develop. 
 
 1 Although Fewkes ('82) identifies his Cassiopea frondosa Lamarck, of Key West and the Tortugas, with Polyclonia 
 frondosa Ag., it is nevertheless a true Cassiopea, not a Polyclonia. 
 
CASSIOPEA XAMACHANA. 193 
 
 Full-grown medusae could be kept in good condition in aquaria for a number of days, 
 and could be kept alive for weeks; while the young medusae and scyphistomas would 
 thrive there an indefinite time, if there were a little pond ooze at the bottom of the 
 aquarium and the water were changed twice a day. Indeed the growth and multiplication 
 of the scyphistomas would proceed actively under these conditions. By keeping the larvae 
 in shallow dishes I was able to watch the whole course of non-sexual development ; but the 
 development from eggs remains unknown to me because of the impossibility of finding any 
 that would develop. It was not until a few days before we left Jamaica in 1891 that I 
 discovered the habit that the very young free-swimming larvae have of hiding beneath the 
 bits of bark and the like to which the scyphistomas in the aquarium were attached, and 
 therefore the greater part of my work on the early stages of development was done during 
 the second expedition. 
 
 After a few words concerning technique I shall begin with a systematic description of 
 the species, followed by an account of the anatomy of the adult, and the remaining part 
 of the paper will contain what I have learned of the development from the observation of 
 the living animals while in Jamaica, and by the study of sections of preserved material, 
 carried on chiefly at the Biological Laboratory of the Johns Hopkins University, but in 
 part also at the Marine Biological Laboratory of Woods Hole and at the Biological 
 Laboratory of the U. S. Fish Commission in the same place. 
 
 I wish to express my thanks to Professor W. K. Brooks for the advice and encourage- 
 ment that he gave me while I was doing this work as one of his students, and I am also 
 indebted to Professor C. 0. Whitman, to the Hon. George M. Bowers, and to Professor 
 H. C. Bumpus for the many courtesies received while at Woods Hole. 
 
 TECHNIQUE. 
 
 For the preservation of the very young larvae a one quarter saturated solution of 
 picric acid, with 2% of sodium chloride added, gave good results. Erlicki's fluid with the 
 same addition, and j% osmic acid followed by Erlicki's fluid, did fairly well for scyphis- 
 tomas, but the best specimens obtained were those killed in the following mixture : 
 10% solution copper sulphate 100 c. c. 
 
 saturated solution corrosive sublimate 10 c. c. 
 
 As soon as they were killed, the specimens were placed in 5% bichromate of potassium 
 and left there until hardened, after which they were washed in 35% alcohol containing a 
 trace of hydrochloric acid and preserved in 70% alcohol. Excellent preparations of the 
 medusae were obtained by this same method, and Flemming's fluid also gave good results. 
 
194 ROBERT PAYNE BIGELOW ON 
 
 SYSTEMATIC PART. 
 
 Genus Cassiopea PERON and LESUEUR (1809). This genus, as limited by 
 Haeckel ('80) , may be defined as follows : Discomedusae without tentacles and without a 
 central mouth opening ; provided ? instead of the latter, with numerous oral funnels at- 
 tached to the ventral, or axial, side of the eight oral arms, which are pinnately or tricho- 
 tomously branched, have a subcylindrical, or subconical, gelatinous support continuous 
 to the tips of the principal branches, are provided with numerous chtb-shajjed vesicles 
 among the oral funnels, and are without appendages on the dorsal, or abaxial, side ; 
 also with four interradial gonads in the aboral wall of the four separate subgenital cav- 
 ities; sixteen marginal sense organs (rhopalia); and thirty-two radial canals connected 
 by a network of anastomosing branches. 
 
 For the sake of clearness this definition is made to include the characters of the 
 family Toreumidae Haeckel, to which this genus belongs, and the purely generic charac- 
 ters are italicized. 
 
 Cassiopea xaxnachana. 1 
 
 Cassiopea xamachana BIGELOW, Zool. Anzeiger, no. 393, 1892, pp. 212-214. 
 
 (?) C.frondosa FEWKES, Bull. mus. comp. zool., vol. 9, no. 7, 1882, pp. 254-259. 
 
 Diagnosis. A Cassiopea with a disc-like umbrella, concave on the aboral side ; 
 when regular, with eighty short and obtuse marginal lobes separated by deep grooves on 
 the surface of the exumbrella (in each of the sixteen parameres three velar lobes between 
 two ocular ones) ; white markings on the exumbrella, consisting of a circular band with 
 a diameter somewhat greater than that of the concavity, within this sixteen oval or elip- 
 tical spots lying in the radii of the rhopalia, and on the outer side eighty marginal spots, 
 one for each marginal lobe ; oral arms rounded and slender, never angular, exceeding the 
 radius of the umbrella by at least one half of its length, and bearing nine to fifteen 
 primary branches which are, in turn, copiously branched, giving the whole appendage a 
 spatulate outline ; very numerous small oval vesicles attached at the axils of the small 
 branches and thickly massed upon the oral disc of adult females, and many small and a 
 few large, flattened, linear vesicles attached one at the axil of each of the larger branches 
 
 1 This name, suggested by Professor Brooks, must stand as printed in the preliminary description of the species, 
 according to the current rules of nomenclature, followed by the Boston Society of Natural History. But it should have 
 been written xamaycana, from Xamayca (the x is pronounced like ch in the German ach), the Indian name for the island of 
 Jamaica, as written by the early Spanish historians (see Herrera, Novi orbis pars duodecima, sive descriptio Indiee occiden- 
 talis, 1024 ; also Encycl. Brit., 9th ed., article, Jamaica). The form Xaymaca given by Bridges, Annals of Jamaica, 1827, 
 and followed by several subsequent authors, is probably a misprint. 
 
CASSIOPEA XAMACHANA. 195 
 
 and to the canals on the oral disc, the thirteen largest vesicles being one at the axil of 
 the largest branch on each arm and one at each junction of the canals on the oral disc; 
 oral funnels entirely wanting on the oral disc in adult females, but present in immature 
 specimens. 
 
 S2)ecial description. A detailed account of the anatomy of this species will be given 
 in the anatomical portion of this paper. It is intended here to call attention merely to 
 the features that distinguish our species from its nearest allies. Cassiojjea xamachana 
 resembles very closely two medusae that inhabit the Red Sea and Indian Ocean, Cassioftea 
 andromeda Eschscholtz and C. polypoides Keller ('83), but it seems, nevertheless, to be 
 distinct from either. 
 
 Upon comparison with the descriptions of Cassiopea andromeda given by Tilesius 
 ('29), Haeckel ('79), and Vanhoft'en ('88), and with the figures of Tilesius ('29) and 
 Forskal (1776) , C. xamachana appears to differ from this species in the following 
 particulars : The exumbrella is not merely flat, but is concave ; besides the ninety-six white 
 spots on the exumbrella, there is a broad circular band of white more or less connected 
 with all of the marginal spots (Fig. 35), the oral arms are more thickly branched and are 
 longer, exceeding by one half to two fifths the radius of the umbrella, instead of being 
 only one third longer ; moreover the arms have none of the flattened appearance figured 
 by Tilesius and mentioned by Haeckel. 
 
 C. xamachana differs from C. polypoides in having more slender oral arms, with five 
 to seven pairs of branches instead of three, and with fewer very large vesicles, and these 
 apparently not so large and always flattened. The color pattern in the two species is 
 nearly the same, except that in C. xamachana the three white spots on the three velar 
 lobes of each paramere are seldom widely separated from the circuLar band of white. 
 The colors in the pattern, however, differ considerably in the two species. The ground 
 color in C. xamachana is never light brown, but is always much darker, a greenish brown, 
 usually with a distinct shade of blue on the subumbrella. The large oral vesicles are 
 never sky-blue, rose-colored nor white, but are yellowish green, often with a bluish green 
 stripe ; and, while the margins of the oral funnels are deep brown, they are always fringed 
 with the white digitella. 
 
 C. xamachana is easily distinguished from C. ornata Haeckel by the presence of 
 large oral vesicles and by the more extensive branching of the arms ; and it differs from 
 C. mertensii Brandt ('38), C. depressa Haeckel ( ? 80), and C. jricta Vanhoffen ('88), in the 
 number of marginal lobes on the umbrella. C. ndrosia Agassiz and Mayer ('99) differs 
 also in number of marginal lobes and in coloring. Fewkes ('82) has described a medusa 
 from Key West and the Tortugas under the name " Cassiopea frondosa Lamarck," which 
 he regards as identical with Polyclonia frondosa Agassiz. From the description given by 
 
196 ROBERT PAYNE BIGELOW ON 
 
 Fewkes it is impossible to identify his species positively. But a comparison of his 
 figures with living specimens of both sexes of P.frondosa shows at once that the two 
 species are distinct ; while a comparison with C. xamachana shows so close a resemblance 
 that I am inclined to think that Fewkes has discovered one of the varieties of our species, 
 described in the next section. Not only is P. frondosa perfectly distinct from C. xama- 
 chana, but I think we are justified in retaining the former, for the present at least, in a 
 separate genus ; and there can be little doubt that Lamarck's Cassiopea frondosa dwell- 
 ing in the "Ocean of the Antilles" with its " margine decem-lobata" is none other than 
 Agassiz's Polyclonia frondosa. Therefore, even if it should be proved that the form 
 described by Fewkes is the same as the subject of the present memoir, the name that I 
 have given to it will hold, nevertheless, as the designation of the species. 
 
 Variations. If we compare the average dimensions of various organs, expressed in 
 thousandths of the diameter, with the maxima and minima, as may be done by examining 
 the third, fourth, and fifth columns in Table 1, p. 201, it becomes evident that there is a 
 very considerable amount of variation in the relative size of parts of C. xamachana. 
 
 In the oral arms, not only does the relative size vary, but the number and the 
 arrangement of the branches are both variable. Moreover this variability exists between 
 the different individuals. In nineteen specimens examined the maximum number of 
 branches found on one arm was sixteen, the minimum nine, and the greatest difference 
 on any one individual was four. 
 
 The most striking variations in C. xamachana, however, are to be found in the 
 structures at the margin of the umbrella. These are highly variable in this species, and 
 have been found to be variable, although to a less extent, in other medusae. It is 
 unfortunate, therefore, that in his beautiful systematic work on the medusae Haeckel 
 should have found himself forced to distinguish the genera chiefly by differences in the 
 marginal structures. He himself notes the variability in the number of parameres of 
 Polyclonia frondosa. Agassiz and Mayer ('99) found in one specimen of C. ndrosia 
 eighteen rhopalia, and in another twenty-two. 
 
 The number of rhopalia was counted in twenty-seven specimens of C. xamachana. Of 
 these ten were found to have sixteen, the typical number for the genus, and twelve had 
 more than sixteen, three having seventeen, and three more, eighteen. The largest 
 number on one individual was twenty-three. There were five specimens with fewer than 
 sixteen rhopalia, but only two had less than fifteen, and both of these showed correlated 
 abnormalities in the mouth parts and subgenital cavities. One had fourteen rhopalia, four 
 oral arms, and two subgenital cavities and gonads. The other had ten rhopalia, only five 
 oral arms, with three oesophageal canals leading from the stomach to the canal system of 
 the arms, and three normal subgenital cavities and one very small vestigial one (Fig. A.) . 
 
CASSIOPEA XAMACHANA. 197 
 
 Redundancy of mouth parts is not nearly as common as of the marginal structures. 
 Only two cases were observed. One specimen with an additional pair of oral arms in one 
 interradius had seventeen rhopalia, The other had eleven arms, with five subgenital 
 spaces and gonads, and this one had twenty-two rhopalia. On the other hand, five speci- 
 mens were found with twenty or more rhopalia, and perfectly normal mouth parts. 
 
 It will be seen, then, that the number of rhopalia, which has been taken as the 
 principal generic character in the group, is a highly variable one. The number of 
 
 Fig. A. Section through the stomach of a specimen with only 10 rhopalia and 5 oral arms, to show the abnormal 
 arrangement of gonadia and oesophageal canals. In the region marked a the margin of the umbrella presents a wide 
 space in which there are no rhopalia. go = gouad. For explanation of the other lettering see Explanation of Plates. 
 
 marginal lobes in each paramere has been taken as one of the principal specific characters, 
 and this is, likewise, highly variable. The variation consists principally in the interpolation 
 of a small secondary lobe between two typical ones. Even in a regular and typical 
 specimen, such as is shown in Fig. 35, the position that would be taken by these secondary 
 lobes is indicated by small ridges on the dorsal surface. A specimen with a large number 
 of rhopalia is as likely to have the marginal lobes in each paramere arranged typically as 
 one having a smaller number. Conversely, a specimen with fifteen to seventeen parameres 
 is as likely as not to vary from the typical form. The variation may consist in the addi- 
 tion of two secondary lobes in the paramere, the addition of four lobes, or in a quite 
 irregular arrangement ; and this modification may affect all of the parameres alike or only 
 a portion of them. 
 
 Throughout all of these modifications of the margins there is manifested a constant 
 regard, as it were, for the symmetry of the parts. It is very seldom that an additional 
 rhopalium appears as if attached fortuitously in some irregular way. Almost always either 
 it is in the midst of an entirely new paramere or else there is a distinct line of symmetry 
 running between two adjacent rhopalia that evidently correspond to an originally single 
 one. In other words, a paramere has been incompletely doubled, and the two parts are 
 
198 ROBERT PAYNE BIGELOW ON 
 
 bilaterally symmetrical to one another. We find all degrees of this doubling in the adult 
 from a double-headed rhopalium 1 to two complete parameres, and the same process may 
 be seen in the forked tentacles frequently found in the larvae (Figs. 14 and 21, x) . With 
 the exception of the forked tentacle and the double-headed rhopalium, these stages of 
 duplication are well represented at ?, w, x, y and z in Fig. 30. 
 
 The radially arranged stripes and spots on the exumbrella, which, with a circular 
 band, form the color pattern described in the next section, vary in number with the 
 rhopalia and marginal lobes. But when two rhopalia are close together there may be 
 only one corresponding rhopalial stripe, and it will then occupy a position intermediate 
 between the two. For example, in the specimen mentioned before as having only ten 
 rhopalia, two of the rhopalia were very close together and there was but one rhopalial 
 stripe corresponding to them. The other rhopalia were evenly spread, except that they 
 were absent from one rather wide section of the circle. The rhopalial stripes, nine in all, 
 were placed in a corresponding manner, and were absent from the corresponding area. 
 
 There is also a wide degree of variation in the extent of fusion between the circular 
 band and the marginal spots. The spots on the velar lobes are usually not fused to the 
 circular band in young specimens, and they frequently remain distinct in adults. It 
 was found, however, that this is more usually true of specimens from the Salt Pond than 
 of those from Port Royal. I thought that I could see, also, correlated differences in the 
 ' sizes of certain of the mouth parts, and I was thus led to inquire if there were a division 
 here of the species into two races. For this purpose Table 2, p. 201, was constructed. 
 From this it will be seen that the specimens from the Salt Pond (var. A) have on the 
 average longer oral arms and shorter vesicles than the ordinary specimens from Port 
 Royal (var. B) , while the stomach is of the same size in the two groups. Whether these 
 slight differences are in any way connected with the probable difference in density of the ' 
 water in the two localities, experiment alone can determine. 
 
 In the third column of this table dimensions are given of some specimens from Port 
 Royal (var. C) that are so different from the rest that they might be regarded as of a 
 distinct species. 4 Suspicion of their being merely sports is aroused, however, by the fact 
 that only two specimens (female) were found living among a large number of the 
 usual form. 
 
 The most striking peculiarity of these two specimens was the great number (forty 
 to fifty) of uniformly large oral vesicles, two to four centimeters in length, scattered over 
 
 1 Fewkes, ('82) has observed similar double-headed rhopalia, and it is on account of the variability of the marginal 
 structures that he regards Polyclonia as merely an abnormal Cassiopea. 
 
 1 It is possible that this variety may be the same as Cassiopea frondosa Lamarck of Fewkes, although his figures do not 
 show any large vesicles on the proximal parts of the oral arms. 
 
CASSIOPEA XAMACHANA. 199 
 
 the whole extent of the mouth parts. Among them the central, radial, and primary 
 vesicles were hardly distinguishable, although so easily recognized by their greater size 
 in the typical form of the species. 
 
 Another peculiarity was a projection of the mesogloea on the oral side of each 
 subgenital osteum, so that the interradial diameter of the oral disc was considerably longer 
 than the radial diameter, as shown in the table. These specimens presented also some 
 peculiarities of coloring, which will be noted in the next section. 
 
 Color. The coloring of this semi-transparent animal consists of certain white mark- 
 ings, together with shadings of subdued tints of brown, green and blue, that are often 
 very beautiful. 
 
 If we turn the aboral side (Fig. 35) of the medusa toward us we find often a brown- 
 ish band encircling the disc at the periphery of the concavity and shading off gradually 
 on both sides. Deeper within the mesogloea there is a much wider white circular band 
 extending under the brownish one ; and white bands, or spots, extend in a radial direction 
 outward from this along the marginal ridges. There is one spot to each ridge, and it 
 reaches nearly to the tip of the marginal lobe. The bands on the rhopalial lobes are inter- 
 rupted, however, by a roughly circular, transparent area over each rhopalium ; and in 
 many specimens, especially young ones, the interrhopalial (velar) spots are not fused with 
 the circle. On the inner side of the circular band of white there is a circle of large white 
 spots, "rhopalial spots," or stripes, that lie deep in the substance of the exumbrella and 
 are visible through the mesogloea, one in the radius of each rhopalium. The spot is 
 elliptical in outline, and extends from the white band to a point about two fifths of the 
 distance between the periphery of the concavity and the edge of the stomach. These 
 spots, while usually continuous with the band, like the marginal spots, are not always so. 
 
 At the centre of the umbrella the stomach and subgenital cavities may be seen 
 through the mesogloea as a reddish brown circular area with a diameter of about one 
 fourth of the total diameter of the disc ; while surrounding the stomach there is a deep 
 blue halo with points that extend outward between the last-mentioned bands of white. 
 
 Now if the animal be allowed to return to its usual position, the subumbrellar surface 
 will be found to be pretty evenly stippled by the greenish brown cells in the mesogloea. 
 Apparently beneath this stippling there is a blue pigment forming a circle around the 
 margin of the stomach and extending outward in broad bands, one along each interrho- 
 palial radius, nearly or quite to a large, more or less distinct patch of blue, that lies close 
 to the margin between every two rhopalia. The radial canals, and the fine, connecting 
 network of tubes, appear as rather indistinct, opaque, white lines. 
 
 The mesogloea of the oral arms is transparent and colorless, except for an opaque 
 white stripe beneath the dorsal surface of each arm., of the same character as the white 
 
200 ROBERT PAYNE BIGELOW ON 
 
 markings of the umbrella. There is a similar stripe on the dorsal side of each of the 
 larger branches which may, or may not, be continuous with the stripe on the main stem. 
 The bases of the oral funnels are of a delicate blue color, which often extends to the 
 brachial canal. The margin of each funnel is a deep brown, that shades off over the 
 blue ; while the small tentacles, or digitella, that spring from this margin are pure white. 
 The larger tongue-shaped vesicles on the arms and oral disc have a greenish yellow color 
 with a bluish green longitudinal stripe. The smaller vesicles on the arms are colored in 
 a similar way and are inconspicuous, but the cluster of very small vesicles that occupy the 
 greater part of the oral disc has a very different appearance, being lightly tinted by line 
 reddish brown pigment spots. 
 
 The two specimens that I have called variety C, are somewhat differently colored. 
 The markings are yellowish white. The circular white band is indistinct. The rhopalial 
 bands are interrupted at the margin of the concavity of the exumbrella, and stop short 
 about half a centimeter from the rhopalial hood. At the margin of the umbrella there is 
 a white spot on each rhopalial lobe and a strap-shaped spot on each velar lobe. The 
 centre of the umbrella is whitish and opaque, so that the stomach does not show through. 
 The oral arms are translucent, milky white tinged with brown, and without distinct white 
 markings, except on the dorsal side of the principal branches. The large oral vesicles 
 are yellow and greenish yellow, with a brown centre. 
 
 Size. The diameter of the largest specimen found is 24 cm., while the smallest 
 specimen that contained eggs measured 6.5 cm. The average diameter of twenty-three 
 adult specimens was 13.7 cm. The relative sizes of the parts are exhibited in the follow- 
 ing tables. Table 1 shows what may be regarded as the normal proportion for the species, 
 though, to be sure, some of the measurements were made only on Port Royal specimens. 
 Some of the dimensions were measured on a smaller number of specimens, and for these 
 the average diameter of the umbrella of the specimens on which these measurements 
 were made is given separately to show the correct proportions. Table 2 furnishes a 
 means of comparing the proportions in the three varieties. 
 
CASSIOPEA XAMACHANA. 
 
 201 
 
 TABLE 1. DIMENSIONS OF SPECIMENS FROM BOTH SALT POND AND PORT ROYAL 
 
 (VARIETIES A AND S.) 
 
 
 Number of 
 specimens 
 measured 
 
 Average di- 
 mensions in 
 centimeters 
 
 Average dimensions 
 in thousandths of 
 average d iameter 
 
 Maximum Minimum 
 
 (In thousandths of diameter 
 unless otherwise noted) 
 
 Remarks 
 
 Diameter of umbrella 
 
 21 
 
 14.33 
 
 1000 
 
 24 cm. 
 
 9 cm. 
 
 
 Length of arms meas- 
 ured from centre of 
 
 
 
 
 
 
 Salt Pond and 
 
 oral disc 
 Length of central 
 vesicle 
 Length of primary 
 vesicle 
 
 21 
 21 
 21 
 
 11.21 
 
 2.71 
 1.82 
 
 782 
 189 
 126 
 
 888 
 287 
 190 
 
 642 
 103 
 71 
 
 Port Royal 
 specimens tak- 
 en together. 
 
 Diameter of umbrella 
 Length of radial 
 vesicle 
 
 10 
 10 
 
 15.79 
 3.01 
 
 1000 
 190 
 
 24 cm. 
 250 
 
 12 cm. 
 117 
 
 Port Royal 
 only. 
 
 Diameter of umbrella 
 
 11 
 
 13.02 
 
 1000 
 
 16.3 cm. 
 
 6.3 cm. 
 
 Salt Pond and 
 
 Diameter of stomach 
 
 11 
 
 4.22 
 
 311 
 
 333 
 
 292 
 
 Port Royal. 
 
 Diameter of umbrella 
 
 3 
 
 18.66 
 
 1000 
 
 24 cm. 
 
 15 cm. 
 
 
 Thickness of umbrella 
 Total depth 
 
 3 
 3 
 
 1.33 
 3.59 
 
 71 
 191 
 
 73 
 212 
 
 70 
 173 
 
 Port Royal. 
 
 Diameter of umbrella 
 Diameter of oral disc 
 
 2 
 
 2 
 
 20.50 
 8.00 
 
 1000 
 390 
 
 24 cm. 
 441 
 
 17 cm. 
 354 
 
 Port Royal. 
 
 TABLE 2. AVERAGE DIMENSIONS OF THE THREE VARIETIES, GIVEN IN THOUSANDTHS 
 OF THE AVERAGE DIAMETER OF THE UMBRELLA. 
 
 
 Variety A Salt Pond 
 
 Variety B Port Royal 
 
 Variety C Port Royal 
 
 Length of arms 
 Length of central vesicle 
 Radial vesicle 
 
 850 
 157 
 
 715 
 
 217 
 190 
 
 818 
 163 
 
 Primary vesicle 
 Diameter of stomach 
 
 112 
 
 298 
 
 138 
 311 
 
 167 
 322 
 
 Thickness of umbrella 
 
 
 
 71 
 
 80 
 
 Total depth 
 Radial diameter of oral disc 
 
 
 
 191 
 390 
 
 213 
 394 
 
 Interradial diameter of oral disc 
 
 
 
 390 
 
 470 
 
 Locality. Great Salt Pond, and mangrove swamps (" The Lakes") in the rear of 
 Port Royal, Jamaica. BIGELOW. 
 
 (?) Moat outside Fort Jefferson on Garden Key, Tortugas Islands, and Mangrove 
 Keys, near Key West, Florida. FEWKES. 
 
202 ROBERT PAYNE BIGELOW ON 
 
 ANATOMY. 
 
 Form of the Body. To one who is familiar with the cyaneas, aurelias, and the 
 like, of our northern coast, the shape of this medusa appears very strange. The aboral, 
 or exumbrellar surface (Fig. 35), instead of being convex in Cassiopea xamnchana, as 
 it is in the great majority of medusae, is concave when the animal is at rest, except for a 
 slight convexity over the stomach, and except in the region of the thinner marginal part 
 of the umbrella, where also it is convex. The surface of the subumbrella, on the other 
 hand, is convex, except in this same thinner marginal area, where it is in turn concave. 
 The umbrella thickens very gradually from its margin to the centre, and the elevations 
 and depressions of its surface have very gentle slopes, so that its general shape is much 
 nearer that of a flat disc than the dome-like form of most medusae (Fig. 35) . 
 
 A circular column arises from the centre of the oral surface of the umbrella. It is 
 broad, but very short; and a few millimeters from the umbrella it loses its circular 
 outline, owing to eight stout arms that spring from it at regular intervals (Fig. 34) . 
 These are smooth and rounded, except along a line on the oral side, where they bear 
 the fringe of oral appendages, and they are long and much branched. This column is 
 the oral disc, and its arms the oral arms. 
 
 The Structure of the Mesogloea. By far the greater part of the mass of the oral 
 arms and disc, as well as the umbrella, is composed of a firm, elastic, gelatinous 
 substance, the mesogloea, and it is to this that the shape of the body is due. 
 
 The description given by Keller ('83), of the structure of the mesogloea in C. poly- 
 poides would apply almost equally well to our species. The mesogloea consists of a 
 hyaline matrix, in which are imbedded certain fibres and three kinds of cellular elements. 
 Most of the fibres appear to be analogous to connective tissue fibres, and take a general 
 course through the mesogloea at right angles to the surface. Others seem to be proto- 
 plasmic. At any rate, they may be observed to proceed from the star-shaped cells that 
 are scattered throughout the jelly. 
 
 The cellular elements are : the star-shaped cells, just mentioned; vesicular bodies, 
 found in certain restricted localities ; and the green cells, which, as it will be shown later, 
 are symbiotic plants. 
 
 The star-shaped cells remind one of osteoblasts, and are probably analogous to them, 
 in that they are concerned in the formation of the jelly. Hamann ('8l) has called 
 them colloblasts. They are small, often somewhat elongated, and have a well-marked 
 nucleus. 
 
CASSIOPEA XAMACIIANA. 203 
 
 The vesicular bodies give rise to the white markings that were mentioned in the 
 description of the species. These vesicles are much larger than the colloblasts. Each 
 one seems to be made up of a wall of exceedingly minute refractile granules, surrounding 
 a clear space. That this body is a cell, however, is shown by the presence of a nucleus 
 pressed closely against one side. 
 
 The green cells, or zoanthelae, are widely distributed throughout the mesogloea, but 
 are most abundant in the umbrella. They are not infrequently found imbedded in the 
 endodermal epithelium. The living cells have a greenish brown color, which they 
 impart to the animal as a whole. They are of considerable size, are globular, 
 without projections of any kind, and are generally to be found in clusters of two or more 
 (za, Figs. 52, 56, and 63) . Each one contains a nucleus and numerous granular bodies, 
 and apparently is surrounded by a cell wall ; but the latter is hard to distinguish from 
 the edge of the adjacent matrix. 
 
 Keller thought that similar bodies in C. polypoides could not be algae, because he 
 failed to find any evidence of a cellulose cell wall. He regarded them, therefore, as 
 essential elements of the " mesoderm." 
 
 In those of my specimens, however, which have been killed in Erlicki's fluid and 
 stained with borax carmine, the nucleus of these cells is found to be red, while the gran- 
 ular contents of the cell are bright green, and there are often one or two green bodies 
 present that are as large or larger than the nucleus. They have all the appearance of 
 chlorophyl bodies, and it is well known that the chlorophyl of some algae is not readily 
 removed by alcohol. Moreover, in teased preparations treated with iodine solution these 
 cells are found to be filled with granules that quickly turn deep blue, evidently starch. 
 The test for cellulose with iodine followed by sulphuric acid, gave, however, unsatisfac- 
 tory results. The outline of the cell would become distinctly darker, but not recognizably 
 blue. In the same way with chloriodide of zinc, a very marked reaction for starch was 
 obtained, the granules becoming almost black ; but so long as the object was viewed 
 by direct transmitted light, no reaction for cellulose could be detected with certainty. 
 On the other hand, when the light was thrown upon the object obliquely by means of a 
 condenser with a central diaphragm, the effect was quite different. The starch granules 
 became a deep ultramarine, and the parts of the cell not occupied by the starch appeared 
 distinctly violet, showing without doubt the presence of cellulose. 
 
 Both starch and cellulose, as well as some form of chlorophyl, having been demon- 
 strated in them, there can be no further question that the green cells in Cassiopea are 
 symbiotic algae. 
 
 The Oral Arms and their Branches. The eight oral arms (Fig. 34) arise from 
 the central oral disc at about equal intervals; and when an arm is extended, the distance 
 
204 ROBERT PAYNE BIGELOW ON 
 
 from the centre of the oral disc to the tip of the arm about equals three quarters of the 
 diameter of the umbrella. But the arms are very contractile, and may be shortened to 
 half this length. The arms are slender and graceful in shape, the mesogloea tapering 
 very gradually to the tips of the finest branches. The branches are arranged alternately. 
 The largest one, which is the first formed, is at a point about two thirds the length of 
 the arm from its base. From this point the branches decrease in size gradually toward 
 the base of the arm, and more rapidly toward the apex. The general outline of the 
 arm, therefore, including its branches, is roughly spatulate. 
 
 The Oral Funnels and Brachial Appendages. Just below the surface of the 
 oral side of each arm there is a longitudinal tube, the brachial canal, that ramifies to 
 each branch, and finally opens to the exterior by funnel-shaped oscula (os., Fig. 34) at 
 the tips of the numerous ultimate branches, and at many places along the course of the 
 tube. The margins of these oscula, or oral funnels, are provided with short tentacle-like 
 projections, the digitella. These are covered by an epithelium containing nettle cells, 
 and each has a gelatinous axis in which there are transverse plates of greater density 
 than the rest of the jelly, and these give the structure the cellular appearance first 
 described by Hamann ('8l) . The epithelium lining the tubes and funnels is 
 ciliated. 
 
 There open also into the brachial canals the lumina of the oral vesicles (v., Fig. 34) . 
 These structures, as already stated in the diagnosis, have their points of attachment in 
 the axils of the branches. All except the smallest are flattened laterally. The smaller 
 ones are oval in outline, the larger ones linear. At one side near the apex there is a 
 cluster of short processes that Hamann has homologized with digitella. 
 
 The Oral Disc. Although the eight oral arms seem to be placed at equal 
 distances and to be alike, they are morphologically in pairs, each pair being homologous 
 to one of the four lips of a semostomous medusa, an aurelia, for example. The line 
 that separates two members of a pair is therefore, according to Haeckel's nomenclature 
 a perradius. The brachial canals from each pair of arms, on entering the oral disc, 
 converge and unite into a single radial tube that is continued to the centre of the disc, 
 where it unites with the other three. In this way the course of the tubes on the oral 
 disc forms a pattern that resembles a Maltese cross. The larger central vesicle is 
 attached at the centre of the cross. In a living specimen 11 cm. in diameter this 
 measured 3 cm. in length. There are four other vesicles that most nearly approach the 
 central one in size, and these arise from the radial canals near the junction of the 
 brachial canals, and I have called them, therefore, the radial vesicles. In full-grown 
 individuals there are eight more vesicles upon the oral disc, a little smaller than the last, 
 one on each brachial canal distal to the junction. It is only near the periphery of the 
 
CASSIOPEA XAMACHANA. 205 
 
 disc that the canals are provided with oral funnels. For most of their course on the disc 
 the canals give rise to the very small vesicles, finely speckled with a reddish brown 
 pigment, that already have been mentioned. These have nettle batteries at their tips, 
 and are so numerous as to cover completely the greater part of the disc and to hide the 
 course of the canals. This mass of small vesicles, however, is not acquired until late. 
 Specimens as much as 6 cm. in diameter will be found to be without them. In such 
 specimens we have the five largest vesicles, and a number of oral funnels are scattered 
 along the canals, just as they are upon the arms. This replacement of the oscula on the 
 oral disc by small vesicles has been observed to occur also on adult females of Polyclonia 
 frondosa, but not in the males (Bigelow, '93) . It is not improbable therefore that a 
 similar difference between the sexes may be discovered in our species of Cassiopea. 
 
 The Subgenital Cavities and the Digestive Tract. At each of the four points 
 of junction of the brachial canals there is a slit-like passage, oesophageal canal, dipping 
 vertically into the mesogloea of the disc, and opening into the stomach. The latter is 
 a lens-shaped cavity, with a gently arched roof. Its floor consists chiefly of four lozenge- 
 shaped areas, where the body wall is very thin and plaited in radial folds (Fig. 34) . 
 These thin parts of the 'body wall form the roofs of the subgenital cavities, which open 
 to the exterior, each by an elliptical orifice, osteum, (x, Fig. 34) in the side of the oral 
 disc near the subumbrella and in the angle between two pairs of arms (interradial) . 
 The gonad appears as a band which crosses this membrane tangentially at its greatest 
 width. Just central to each gonad there is a multiple series of very many small gas- 
 tric filaments forming a narrow band parallel to the ovary. These are ciliated, and 
 provided with nettle and gland cells. The portion of the floor of the stomach not made 
 up of these lozenge-shaped membranes is bounded by the firm mesogloea of the oral disc. 
 This area has the shape of a Maltese cross, and it is in the arms of this cross, between the 
 subgenital cavities, that the passages from the oral canals open into the stomach. 
 
 Near its periphery the floor of the stomach is marked by radial grooves. These are 
 continued, each into one of the radial canals that extend outward from the edge of the 
 circular stomach to the marginal region of the umbrella. There are regularly thirty-two 
 of these, sixteen in the radii of the rhopalia, and sixteen interrhopalial. When the 
 number of rhopalia is increased, the number of radial canals may or may not increase in 
 proportion. There are often thirty-four or thirty-six of them. The canals in the 
 radii of the rhopalia are larger and more nearly straight than the interrhopalial ones, and 
 all are connected by a fine network of anastomosing branches, among which no distinct 
 circular canal can be recognized. The meshes in the network of canals are connected by a 
 plate of endodermal cells, the endodermal lamella. This lamella is also in contact with the 
 subumbrellar ectoderm along a line encircling the umbrella a short distance from its mar- 
 
206 ROBERT PAYNE BIGELOW ON 
 
 gin, so that there is a complete sheet of endodenn separating the subumbrellar from the 
 exumbrellar mesogloea. 
 
 Musculature. The exumbrella is devoid of muscles, but on the opposite side 
 there is a continuous sheet of muscle fibres, which is spread over the subumbrella, 
 except a narrow zone at its margin, and is continued over the oral arms to their finest 
 ramifications, and also into the subgenital cavities. 
 
 Most of the fibres on the subumbrella do not take an evenly circular course, but are 
 undulating. They form in this way a series of double " arcades " like those found by 
 Haeckel in other species of Cassiopea. There is one of these double arcades for each 
 interrhopalial space. The surface of the mesogloea in this region is grooved. The 
 sheet of muscle fibres lies directly upon it, and is therefore corrugated, the grooves 
 being parallel with the fibres. 
 
 The muscular layer upon the oral arms is smooth, and its fibres take a longitudinal 
 course, extending to the digitella and oral vesicles. 
 
 In the subgenital cavities the arrangement of the muscle fibres could not be made 
 out; but their presence was revealed by the squirming movements of the thin membrane 
 that separates the subgenital cavity and bears the gonads and gastric filaments. 
 
 Structure of the Marginal Sense Organs. Each rhopalium has a pigment spot 
 on the aboral side near the extremity, and each one lies in a deep sensory niche. The 
 dorsal sensory groove, common in the Pelagidae, Aurelia, etc., is entirely lacking; 
 although Keller found in C. polypoides a slightly depressed thickening of the ectoderm 
 that corresponds to it. The sensory niche and rhopalium are, with the exception of the 
 pigment spot, similar in all essential particulars to those found in Pelagia. The 
 rhopalium is the only organ in the sensory niche (Fig. 56). It is a hollow, finger-like 
 projection attached by its base to a low ridge that runs along the roof to the central wall 
 of the niche. This ridge is penetrated longitudinally by the continuation of a radial 
 canal from the stomach, and the lumen of the rhopalium opens into the distal end of this 
 canal. In the distal half of the rhopalium the lumen is nearly obliterated by the increase 
 in thickness of its endodermal lining. Here the endoderm, instead of being a columnar 
 epithelium as elsewhere, is a mass of parenchyma-like cells, each of which contains a 
 large calcareous concretion, a so-called otolith. A thin, supporting membrane separates 
 the endoderm from the ectoderm. At the distal extremity of the rhopalium the ecto- 
 derm is a thin, cuboidal epithelium, while over the rest of the surface it is a thick, sensory 
 epithelium resting on a thick network of fine nerve fibres. This, in turn, rests on the 
 supporting membrane. I have observed no ganglion cells in this layer of nerve fibres, 
 which is continued under the epithelium of the rhopalial ridge to the central wall of the 
 niche, where it becomes imperceptible. There are no thickened bands of these fibres 
 
CASSIOPEA XAMACHANA. 207 
 
 running to ciliated pockets, such as are found in Dactylometra (Bigelow, '90), and the 
 fibres probably spread out finally into a thin network underlying the general epithelium 
 of the subumbrella. 
 
 The one feature in which this rhopaliurn differs from what is found in Pelagia is the 
 presence of the pigment spot, already mentioned, lying on the aboral side of the 
 rhopalium immediately above the centre of the mass of concretions. This area is 
 probably sensitive to light, but it only differs from the rest of the sensory epithelium in 
 that here the superficial cells are deeply colored by a yellowish brown pigment. A 
 more careful examination would undoubtedly show the histology of this structure to be 
 similar to what Schewakoff ('89) has found in Aurelia. 
 
 HABITS. 
 
 The species of Cassiopea and the closely related genus Polyclonia find their habitat 
 usually in quiet lagoons among the mangroves along the shores of the tropical seas. The 
 mode of life of several species has been described by Brandt ('38) on the authority of 
 Merten.s, L. Agassiz ('62), Gray ('69), A. Agassiz ('8l), Archer ('8l),Fewkes ('82), Guppy 
 ('82) , and Agassiz and Mayer ('99) . Cassiopea xamachana is no exception to the rule 
 either in its habitat or its sedentary mode of life. 
 
 When the young medusa is set free from the strobila it is an active swimmer. It 
 gradually becomes less active as the mouth parts acquire their adult structure, and by 
 the time the animal has reached a diameter of two centimeters it has definitely taken 
 up its abode upon the bottom. It lies there, as described in the Introduction, with the 
 oral appendages upward, and seldom changes its position unless disturbed. The con- 
 cavity of the exumbrella is an important aid in maintaining this posture against the 
 action of waves and currents. The gelatinous tissue is firm and elastic, and causes the 
 umbrella to assume its normal shape when the subumbrellar muscles are relaxed. The 
 slight suction thus produced when the medusa comes to rest on a flat surface gives it 
 such a hold that a certain amount of force is required to remove it. 
 
 Usually, however, the water in the lagoons is very quiet, and there is more danger 
 from its stagnation than from its motion. A Cassiopea is enabled to avert this danger by 
 the slight swimming movements of the thinner marginal part of the umbrella. By 
 means of these rhythmic contractions the water is drawn in on all sides, and then is 
 driven upward and away. A healthy specimen lying undisturbed on the bottom of an 
 aquarium was observed during seven minutes to make on the average 19.7 contractions 
 of the umbrella per minute. In this way the animal is enabled to draw to itself a fresh 
 supply of oxygen and of its minute food material. 
 
208 ROBERT PAYNE BIGELOW ON 
 
 The oral arras and their branches are usually spread out so as to cover the sub- 
 umbrella completely, but they are almost always in motion, bending to one side or the 
 other, and they may be flexed aborally until the tips come within the umbrellar 
 margin, or extended until they reach far beyond. Besides these general movements, 
 the various appendages of the oral arms have movements of their own. Muscular con- 
 tractions may be observed also in the thin membrane that separates the stomach from 
 the subgenital cavities, and they probably serve to renew the water that bathes the 
 gonads. 
 
 When the oral disc has been severed from the umbrella, both parts may remain 
 alive for several days, and both retain their powers of spontaneous movement. The first 
 effect of the operation is often to throw all of the parts into a strong tetanus, but shortly 
 afterwards the pulsations of the umbrella may be renewed at a rate considerably more 
 rapid than normal, 32 to 34 per minute in one case. When the medusae have been 
 for some time under unfavorable conditions, it frequently happens that the part of the 
 body-wall surrounding the periphery of the stomach is ruptured, and thus the mouth parts 
 as a whole become separated automatically from the umbrella. 1 
 
 While at Bimini, Bahamas, in 1892, I observed that the food of Polyclonia f rondo sa 
 consists chiefly of copepods and other small Crustacea, and that these are caught by the 
 combined action of the oral vesicles and the oscula ('93, p. 106). If a copepod strikes 
 a vesicle, the vesicle bends quickly so as to cover the mouth of the adjoining oscu- 
 lum, and the copepod is thus enclosed in a trap. Artificial stimulation would cause the 
 same reaction. 
 
 Experiments on Cassiopea xamachana made to determine whether or not this 
 species obtains its food in the same way gave negative results. Stimulation of an oral 
 vesicle causes only a slight bending on the side stimulated. Although these vesicles are 
 provided with batteries of nettle cells near the tip, I was unable to see that they played 
 any part in the taking of food. It may be that they are protective, but the sting is 
 very feeble. 
 
 Examinations of the contents of the stomach were almost equally unsatisfactory. 
 The contents of twenty-two stomachs were examined, and of these fourteen contained 
 only a clear, very viscous fluid and, in some cases, a few apparently ripe eggs, more or 
 less distorted, some small, colorless cells, probably sloughed off from the endodermal 
 epithelium, and green cells identical with the " zoanthelae '' found in the mesogloea. One 
 or more copepods and other Crustacea were found in five specimens. In one of these one 
 small amphipod was found, and in another the cornea of an unknown crustacean. 
 
 1 While^this paper is passing through the press a paper has appeared by E. W. Berger (1900), in which lie gives the 
 results of experiments made by F. S. Conant upon Polyelonia and Cassiopea to test the effect of removing the rhopalia. 
 
CASSIOPEA XAMACHANA. 209 
 
 Diatoms and other algae, exclusive of the above-mentioned zoanthelae, were found 
 in four cases out of the twenty-two. Almost always the first impression on opening a 
 stomach was that it was empty; and it was only by careful examination that the contents 
 of the stomach could be discovered. In two cases, however, a considerable amount 
 of material was found in the stomach. In one of these the stomach contained, besides 
 the usual eggs, zoanthelae, debris, etc., the remains of many copepods, some nematods, 
 a zoea, and some diatoms. In the other one there was found a compact greenish mass, 
 about one centimeter in diameter, composed of granular debris and diatoms of various 
 species, together with some desmids, Oscillaria, foraminifera, infusoria, Vorticella, and 
 some fine filaments with spirally arranged contents. 
 
 This species exhibits the power of regeneration of lost parts to a marked extent. 
 Specimens were frequently met with in which branches of the oral arms, or even portions 
 of the margin of the umbrella, had evidently been formed recently to replace parts that 
 had been destroyed. Moreover, branches of the oral arms that had been cut off were 
 observed to regenerate oscula and vesicles at the central end. 
 
 ONTOGENY. 
 
 Historical Review. Numerous studies upon the reproduction of various animals 
 by budding have shown that the formation of organs in the bud may take an entirely 
 different course from the development of homologous organs in the sexually produced 
 embryo. As the observations to be described in the sequel were made entirely upon 
 larvae that were observed, or supposed, to be asexually produced, they cannot settle 
 any of the disputed points in regard to the development of sexually produced larvae. 
 Nevertheless it will be of interest to compare the sexual with the asexual mode of 
 ontogeny, especially as the development of a scyphistoma from a bud has never before 
 been fully described. 
 
 The development of scyphomedusae from the egg has been studied in comparatively 
 few forms. Several species of Aurelia have been studied by Sars, Haeckel, Schneider, 
 Glaus, Goette, Frank Smith, and Hyde. Two species of Cyanea have been studied by 
 McMurrich and Hyde. A species of Chrysaora has been studied by Glaus; and 
 Kowalewsky, Metschnikoff, Krohn, and Goette have traced the very interesting abbrevi- 
 ated development of Pelagia noctiluca. The nearest ally of our species that has been 
 studied with any degree of completeness is the Mediterranean rhyzostome Cotylorhiza 
 tuberculata, which has been the subject of investigation by Glaus and Goette. 
 
 From the description of the process of budding given in the- next section, it will be 
 
210 
 
 ROBERT PAYNE BIGELOW ON 
 
 d- 
 
 d 
 
 noted that the larvae produced by budding are set free in a form resembling planulae, 
 
 and it is the planula stage in sexual reproduction which is the earliest that can be 
 
 compared with any stage to be described in this paper. 
 
 All agree that the planula of the Scyphomedusae is a more or less oval, ciliated 
 
 larva, somewhat flattened on one side. It consists of two layers of cells surrounding a 
 
 cavity which is completely shut off from 
 the exterior. The first step toward the 
 development of the scyphistoma is an in- 
 vagination of the ectoderm at the posterior 
 pole of the planula. According to Goette 
 and Miss Hyde, the endoderm is invagina- 
 ted at the same time in such a way that 
 two endodermal pouches remain in the 
 plane of the long diameter, "Haupte- 
 bene," Goette, (Pig. B, and b-b Fig. 
 D), one on each side of the invagination, 
 while the endoderm is pushed entirely 
 away from the oral pole in the plane of 
 the short diameter (Fig. C, and c-c Fig. 
 D) . The ectodermal invagination is the 
 oesophagus (Schlund) , its external open- 
 ing is the mouth, and the endodermal 
 evaginations are the first pair of gastric 
 pouches. Soon an opening is formed 
 (Schlundpforte) between the base of the 
 oesophagus and the central stomach, and 
 at the edge of the opening the ectoderm 
 fuses with the endoderm. Then the sec- 
 ond pair of gastric pouches is formed. 
 According to Goette these are produced in 
 Cotylorhiza and Pelagia entirely from the 
 
 g 
 
 Figs. B-G. Two stages in the development of the mouth 
 and gastric pouches in a sexually produced scyphistoma, 
 according to Goette. Figs. B to I) are sections in the three 
 dimensions of space of a larva in which the oesophagus is 
 invaginated and the first pair of gastric pouches are formed. 
 Figs. E to G are similar sections of a larva in which the open- 
 ing from the oesophagus into the stomach (Schlundpforte) has 
 been established and the second pair of gastric pouches are in 
 the process of formation. 6, c, d, etc., indicate the plane of 
 Figs. B, C, D, etc. 
 
 opening (Schlundpforte) , and are therefore 
 at the level of the upper edges of the first pair of pouches. As these pouches extend out- 
 
 ectoderm of the lower part of the oesopha- 
 gus (Fig. F) . According to his view the 
 lower edges of these evaginations coincide . 
 with the margin of the gastro-oesophageal 
 
CASSIOPEA XAMACIIANA. 211 
 
 ward the ectoderm is pushed out until the principal radii) e-e and f-f, Fig. G) gradually 
 become' equal. This results in the formation of the flattened peristomal disc (Figs. E 
 and F) . At the same time the wall separating the oesophagus from the first pair of gastric 
 pouches (Taschenvorhang) is split upward until the openings into the two pairs of pouches 
 are upon the same level, and the " Taschenvorhang " is reduced to a low ridge, while the 
 oesophagus is very much shortened. Portions of the original lining of the lower part of 
 the oesophagus persist as the covering of the inner edges of the septa which separate the 
 four gastric pouches. The larva is now in what Goette calls the scyphula stage. He 
 regards this stage as of great phylogenetic importance, showing clearly, he thinks, a 
 close genetic connection between the Scyphomedusae and the Anthozoa ; so that these 
 groups should be placed in a single class, Scyphozoa, to distinguish them, on the one 
 hand, from the Hydrozoa, including the hydroids, hydromedusae, and, on the other, from 
 the Siphonophorae. 
 
 This view, which is confirmed by Miss Hyde, is antagonized by Glaus, and has given 
 rise to a prolonged controversy. The parties to this dispute are practically in accord 
 in regard to the facts of observation, as represented by the figures in their latest 
 contributions. It is in the interpretation of these facts that they differ mainly. Glaus 
 ('90) admits that there is an ectodermal invagination previous to the formation of the 
 mouth, and that the lining of the proboscis is ectodermal. He maintains, however, that 
 the condition represented in Figs. B, C, and D, is due to a severe contraction of the 
 animal, and is without morphological significance. He denies that there is any 
 oesophagus, " Taschenvorhang," or " Schlundpforte," in the sense that Goette uses these 
 terms ; and with these he rejects the idea of a close affinity between the Anthozoa and 
 scyphomedusae, with the correspondingly sharp distinction between the latter and the 
 hydromedusae. He admits, however, that a distinction of importance between scyphis- 
 torna and hydropolyp is to be found in the possession by the former of an ectodermal 
 lining of the proboscis, and in the presence of gastric pouches and septa. 
 
 Goette's position has been strengthened considerably by his latest contribution on 
 this subject ('93), and his conclusions are confirmed in nearly every particular by Miss 
 Hyde. Goette's figures appear to be camera drawings of serial sections, and are a 
 great improvement over the rather diagrammatic illustrations in his earlier papers. 
 They are not entirely convincing, however, for the ectoderm and the endoderm grade 
 into each other so that it is impossible to determine the exact boundary ; and the 
 material is so subject to distortion during the preservation that it is often difficult to 
 determine whether a given fold of the epithelium is of morphological value or is merely 
 an artifact. 
 
 Miss Hyde fails to confirm the view that the whole of the second pair of gastric 
 
212 ROBERT PAYNE BIGELOW ON 
 
 pouches (and hence, according to Goette, five eighths of the peripheral digestive tract of 
 the medusa) is of ectodermal origin. On page 550 of her paper she speaks of only the 
 roof, i. e., the lining of the oral side, of these pouches as formed from oesophageal ecto- 
 derm, and her sections bear out this view. 
 
 The foregoing brief summary of the present state of knowledge regarding the early 
 stages in the development of the sexually produced scyphistoma will serve as an 
 introduction to what is to follow. Mention of the work of others upon the later stages 
 will be made when we come to the corresponding periods in the development of 
 Cassiopea xamachana. 
 
 The Formation of the Bud. In 1841 Sars described the budding of scyphistomas 
 that were supposed to belong to a species of either Aurelia or Cyanea. The buds, accord- 
 ing to this account, may grow out directly from the main part of the body of the larva, 
 or they may be produced on stolons extending outward from the foot. In either case, 
 several buds may be formed, apparently in various positions on the scyphistoma at one 
 time. The figures show the buds attached to the parent and provided with a well- 
 developed crown of tentacles at the distal end. Agassiz ('60) found a similar process of 
 budding to occur occasionally in Aurelia. Goette ('87) has confirmed these observations, 
 and has found that the larvae of Cotylorhiza tubereulata also produce buds. 
 
 In Cotylorhiza the bud is formed as an outgrowth from the body of the scyphistoma ; 
 and as it grows it gradually approaches the shape of its parent, but its relative position is 
 just the reverse of what Sars found ; for the distal end forms the stem, and the proximal 
 end begins to flatten out into a circumoral disc. In this condition the bud is set free, and 
 swims about, rotating on its long axis, with its distal end forward. The mouth is formed 
 at the point where the constriction finally separates the bud from its parent, and the larva 
 fixes itself by the opposite end. 
 
 Glaus ('92) has found that the scyphistomas of Cotylorhiza not only produce buds, 
 but that they produce them in large numbers. Scyphistomas reared from eggs that had 
 been laid in September, 1890, were kept alive in the aquaria at Trieste and Vienna 
 throughout the following winter and spring. No change was observed after the larvae 
 had reached the sixteen-tentacle stage, until the following July, when budding occurred. 
 The process was not restricted to a few well-nourished individuals, but seemed to be a gen- 
 eral and repeated phenomenon, and it resulted in a large increase in the number of larvae. 
 Claus's brief description of the formation and fate of the bud, accompanied by three 
 figures, corresponds perfectly with what I have to describe in the following pages. The 
 strobilization, he says, took place in August, and was monodiscous. 
 
 Another case of rapid multiplication of scyphistomas by budding is described by 
 Lacaze-Duthiers ('93) . A colony of these larvae, of unknown origin, was discovered in 
 
CASSIOPEA XAMACHANA. 213 
 
 an aquarium at Banyuls in 1892. No strobila or ephyra was observed up to October, 
 1893, but in the meantime the number of scyphistomas had increased enormously. The 
 buds appeared as elevations on the side of large individuals. The base of this elevation 
 became elongated into a filamentous stolon carrying the bud at its tip. The bud fixed 
 itself to the glass, gradually developed tentacles, and finally became independent by the 
 disappearance of the stolon. 
 
 In Cassiopea xamachana the process of budding is an important, if not the chief, factor 
 in the perpetuation of the species. On looking over collections of scyphistomas taken 
 from the Great Salt Pond during May, June, and July, a considerable number was found 
 with buds attached in various stages of development (Figs. 1, 2, and 26), and budding 
 continued in the aquaria. 
 
 There is no stolon. The first visible rudiment of the bud is a slight swelling on one 
 side of the calyx just above where it tapers into the stem. It involves all three layers of 
 the body wall (Fig. 36) . At an early stage in the growth of the bud the four septal 
 muscles may be found as four slender cords of cells embedded in the mesogloea and appar- 
 ently growing out from a thickened area of the ectoderm at the apex of the bud (sm, 
 Figs. 38 and 39) . This appearance seems to indicate that the septal muscles of the bud 
 are formed, as in sexually produced scyphistomas, by an ingrowth of the ectoderm. 
 
 Careful study of serial sections through young buds shows, however, that the 
 septal muscles of the bud are connected with septal muscles of the parent. In 
 Fig. 37 the course of the septal muscles is reconstructed from a series of longi- 
 tudinal sections. The muscle sm t passes around the base of the bud on the side 
 away from the observer and gives rise to two branches, sm\ and sm' 3 . These extend 
 toward the apex of the bud, and each one divides dichotymously. Muscle sm 4 gives 
 off a branch which fuses with sm^ at the base of the bud. Sm 2 produces three branches 
 which unite into a single branch. This branch extends into the base of the bud, but it 
 was impossible to trace it further. It may be connected, perhaps, with the muscle sm' 2 , 
 which was traced for a short distance from the apex of the bud. 
 
 On account of the presence of the muscles, it is possible to study the relation of the 
 plan of symmetry of even young buds with the symmetry of the parent. A series of 
 sections made at right angles to the long axis of the bud shows that the vertical perradii 
 of the bud lie in the plane of one of the perradii of the parent. But in transverse 
 sections it is impossible to trace the muscles of the bud, except for short distances, 
 owing to their extreme fineness. 1 
 
 However, the study of longitudinal sections makes it reasonably certain that the sep- 
 
 1 The position of the bud is always perradial, although in some preparations it appears to be interradial, owing to the 
 obliquity of the sections, as in Fig. 36, 
 
214 ROBERT PAYNE BIGELOW ON 
 
 tal muscles of the bud are derived from outgnnvths of one or both of the septal muscles of 
 the parent which lie in the interradii adjoining the perradial area of bud formation. If this 
 be true, then every part of the young bud is formed from the corresponding part of the 
 parent, viz., ectoderm from ectoderm, mesogloea from mesogloea, endoderm from endo- 
 derm, muscles from muscles, and digestive tract from digestive tract. There is no indica- 
 tion of any method of budding of the kind described by Lang ('92) . 
 
 In the young bud the mesogloea is very thin, so that the ectoderm and endoderm are 
 very nearly in contact. The evagination gradually increases in size, becoming first hemi- 
 spherical and then more elongated. At the same time a constriction appears close to the 
 body of the scyphistoma, which deepens until the bud becomes a spindle-shaped body 
 attached to its parent by a short and narrow stem consisting of a film of mesogloea 
 covered with ectoderm, the digestive cavity of the bud being entirely closed (Fig. 1) . 
 
 Scyphistomas are never found with more than two buds attached. When two bvids 
 are present they are always of different ages, and the elder is always attached to the 
 apex of the younger (Fig. 2) . 
 
 The Planula-like Larva. When finally constricted off, the bud is a simple, spindle- 
 shaped, hollow body, without trace of mouth or tentacles. It is like a planula in form and 
 habits. The whole surface is covered with cilia, and it swims about,- rotating from right 
 to left upon its long axis. In swimming, the distal end is directed forward. While swim- 
 ming, the larva is constantly changing its shape, assuming in a few minutes various forms 
 from an elongated spindle to a short heart-shape (Fig. 3, A, B and (7) . It swims near 
 the bottom, hiding under any object that it may find there. When it strikes an 
 obstacle, it may rest there quietly, or it may rotate slowly upon its long axis. In all 
 its movements it reminds one very strongly of Agassiz's description of the planulae 
 of Aurelia. 
 
 The larva is white, speckled with a few greenish brown spots. It is rather opaque, 
 but much of the structure may be seen in a living specimen. A longitudinal section shows 
 that the ectoderm consists of a deep layer of very narrow and clos.ely-packed columnar 
 cells (Fig. 39) . The mesogloea contains a few green cells (producing the greenish brown 
 spots), and some widely scattered colloblasts. The layer is thickest at the equator, 
 diminishing gradually to a very thin layer at both ends. The four septal muscles (am) 
 are seen clearly at the distal end of the larva, embedded in the mesogloea and united with 
 the ectoderm near the apex (Fig. 38) . In one specimen, not yet detached from the 
 parent, it was possible to trace one of the muscles all the way from the proximal to the 
 distal end. The muscle fibres are already differentiated and line the tube of mesogloea, 
 while the nuclei occupy a central position. 
 
 The endoderm is a columnar epithelium, rather thin, with the cells closely packed 
 
CASSIOPEA XAMACHANA. 215 
 
 together and coarsely granular at the proximal or posterior end of the larva. Toward 
 the equator the cells become higher ; and at the distal, or anterior, end they are large and 
 clear. The character of the endoderm makes it possible to identify the anterior end of 
 the swimming larva with the distal end of the bud. 
 
 The Formation of the Mouth. The first change to be seen in the swimming larva 
 is the formation of the mouth, which occurs two or three days after the larva has been set 
 free. When writing my preliminary paper ('92 a) , I was in doubt as to the relation 
 between the poles of the bud and those of the larva. The better and more abundant 
 material obtained during the second visit to Jamaica proved conclusively that the proxi- 
 mal end of the bud forms the oral end of the larva, just as it does in Cotylorhiza, accord- 
 ing to Goette. The identification is made easy by the polar differentiation of the 
 endoderm described in the previous section. 
 
 When first seen the mouth looks like a minute pin-hole in the posterior end of the 
 larva (m, Fig. 4 B) . In longitudinal sections at this stage the first indication of the for- 
 mation of the mouth is the disappearance of the mesogloea from a small area at the poste- 
 rior end, so that there is no longer a distinct boundary there between the ectoderm and 
 endoderm (m, Fig. 40) . At the same time a small dent appears in the outer surface. 
 This deepens until it forms a minute tube connecting the endodermal cavity with the 
 exterior (Fig. 41) . The mouth thus formed gradually widens and becomes slightly 
 funnel-shaped. 
 
 Further stages in the development of the mouth are represented in Figs. 5, 6, 7. In 
 In Fig. 6 there is a distinct circular groove which outlines the base of the proboscis and 
 separates it from a rudimentary peristome. In Fig. 7 the peristome is well developed, 
 and the mouth is widely open. 
 
 There is no invagination of the ectoderm connected with the formation of the mouth, 
 and there is no oesophagus, " Schlundpforte " or " Taschenvorhang." So, if Goette's 
 account of the formation of the mouth in the sexually produced scyphistomas be accepted, 
 we have here a case where an agamogenetic differs to a marked degree from the 
 gamogenetic course of development. 
 
 The Scyphistoma. With the elongation of the forward end, the formation of ten- 
 tacles, and the development of four gastric pouches, the free-swimming larva becomes a 
 typical scyphistoma. 
 
 By the end of the third or fourth day after the bud has been set free, the forward 
 end of the larva has elongated to form a stem equal in length to the rest of the body 
 (Figs. 7, 8,, 9, and 11) . The end of the stem becomes expanded, generally flattened, and 
 the epithelium covering it becomes deeper than the rest (Fig. 42) . This epithelium pro- 
 duces a secretion which serves to fasten the larva to some solid object. Fixation usually 
 takes place during the fourth or fifth day, but the time varies greatly. 
 
216 ROBERT PAYNE BIGELOW ON 
 
 Development of the Tentacles. During the third day the peristome appears as a minute 
 ridge surrounding the posterior end of the larva, a short distance from the mouth. The 
 first series of tentacles arises during the following twenty-four hours as four perradial 
 angles in the margin of the peristome (Fig. 8) . Four interradial tentacles appear almost 
 simultaneously with these, or sometimes considerably later (Figs. 9, 10, 11, and 12) . 
 The elongation of the tentacles takes place rapidly, so that at about the end of the sixth 
 day the peristome is surmounted by a crown of eight tentacles, which equal the proboscis 
 in length. 
 
 With the broadening of the peristome the differentiation of the body of the scyphis- 
 toma into stem and calyx becomes apparent externally (Figs. 13 and 14) . When the 
 eight perradial and interradial tentacles have become long enough to reach some distance 
 beyond the mouth, eight adradial tentacles appear in the angles between them. In 
 Fig. 14 the adradial tentacles are distinctly developed, and two of the tentacles of the first 
 series are bifurcated near the base. Figs. 15 and 16 represent the typical scyphistoma in 
 the sixteen-tentacle stage. The tentacles are now long and graceful, and thickly dotted 
 with batteries of nettle cells. 
 
 When fully developed, the scyphistoma is about one millimeter and a half in diameter ; 
 and it is provided typically with thirty-two tentacles. 1 But there is as much variation in 
 the number of tentacles in the scyphistoma as there is in the number of sense organs and 
 parameres in the adult. The number of tentacles is seldom less than thirty-two, often 
 greater. The way in which this variation takes place is indicated in Figs. 21 and 14. 
 All degrees of anomaly maybe observed, from a bifurcated tentacle shown at x in Fig. 21, 
 through the condition represented in Fig. 14, to two completely separated tentacles occu- 
 pying the position of one typical one. 
 
 The tentacles of a well-developed scyphistoma, when fully expanded, exceed the 
 length of the body several times. According to the position in which they are held, the 
 tentacles may be divided into two series. Those of one series are held nearly erect, while 
 those of the other series, consisting of the alternate tentacles, are bent backward until 
 their tips nearly touch the ground upon which the animal rests. The action of the ten- 
 tacles in capturing prey may be observed in a small aquarium, under the microscope. As 
 soon as a tentacle comes into contact with a small floating body, such as a copepod, it is 
 whipped quickly into the mouth, and at the same instant the side of the mouth toward 
 the tentacle is opened more widely. On one occasion I saw two tentacles make captures 
 at the same time, and the mouth expanded in both directions at once, showing a close 
 co-ordination between the movements of the tentacles and of the mouth. 
 
 1 Specimens have been found with twenty-four tentacles, but it is uncertain whether this is a regular stage in develop- 
 ment between the sixteen- and thirty-two-tentacle stage, or a duplication of tentacles of the earlier stage. 
 
CASSIOPEA XAMACHANA. 217 
 
 Development of the Gastric Pouches. While the final result is the same, the method 
 of development of the gastric pouches differs entirely in our larva from the process as 
 described by Goette. The free-swimming larva is somewhat flattened laterally (Fig. 4) , 
 and the long and short diameters are in the planes of the perradii. But there is no 
 evidence that the gastric pouches in the long diameter are formed any earlier than those in 
 the short diameter, and the ectoderm plays no part in their development. The formation 
 of the gastric pouches is usually described as a process of evagination ; but in this case, at 
 least in the earliest stages, the delineation of the pouches seems to be due rather to the 
 ingrowth of the septa. 
 
 These appear at the time of the formation of the first tentacles (Fig. 8) as four 
 minute vertical folds of the endoderm (sep, Fig. 43) , placed equidistantly in the angle 
 formed by the peristomal fold (compare Fig. 42) . The mesogloeal portion of the septum 
 is at first very thin, and in the four-tentacle stage (Figs. 8 and 43) is no higher than the 
 thickness of the endodermal layer of cells. The septal muscles do not penetrate the septa 
 at this stage. While well-developed below, they can be traced upward only to within 
 35 or 41 p. * from the base of the septa. 
 
 In the eight-tentacle stage (Fig. 13) the septum is still very small, and the septal 
 mesogloea near the margin of the peristome is very thin, hardly thicker than a cell wall. 
 But at the central margin it has increased in thickness, and now the septal muscle may 
 be traced from the stem upward through this thickened portion of the septal mesogloea to 
 the peristomal ectoderm (sm, Figs. 44 and 47). It is impossible to determine whether 
 the new portion of the septal muscles is formed by growth upward of the muscles already 
 present in the stem, or whether it is the result of a proliferation of the peristomal ecto- 
 derm which may grow downward and fuse with the older portion of the septal muscles. 
 
 The four septa are now complete, and divide the digestive cavity into a large 
 central stomach, extending into the stem, and four shallow marginal gastric pouches. 
 The gastric pouches expand with the growth of the peristomal disc, so that the ecto- 
 derm and endoderm remain in close contact at the margin ; while the central edges 
 of the septa retain their original relative position. Thus the gastric pouches and the septa 
 become deeper as the larva increases in size. This is evident in the sixteen-tentacle stage 
 (Figs. 15 and 45 to 49) . It will be shown later that the relation of the interradial ten- 
 tacles to the septa is variable. In this stage, however, the distal part of the septal meso- 
 gloea has begun to disappear, so that immediately under the interradial tentacles the 
 endoderm of adjacent pouches is fused (Figs. 45, 46, and 47) . In the fully developed 
 scyphistoma this area of fusion is perforated, so that there is a communication between 
 adjacent pouches, forming the " Eingsinus " of German authors. In the specimen with 
 
 1 35 or 41 (i = about one seventh of the length of the larva. 
 
218 ROBERT PAYNE BIGELOW ON 
 
 forty-two tentacles, from which the section represented in Fig. 51 was taken, this per- 
 foration was very small. Figs. 52 and 53 represent a little later stage, in which the 
 opening has become much wider. 
 
 Each septal muscle is a solid cord of cells, with a single layer of longitudinal muscle 
 fibres in its periphery. In the peristome the fibres of the septal muscles spread out in a 
 fan-shaped arrangement toward the margin. 
 
 Four slight interradial depressions in the peristome may be observed as early as the 
 four-tentacle stage. They are deeper in the eight- and sixteen-tentacle stages, and the 
 septal muscles may be seen to join the ectoderm at their bottoms. These depressions may 
 be homologous with the septal funnels of the Stauromedusae, or they may be merely the 
 result of the contracted condition of the larva. The question is of no importance, for 
 there can be no doubt about the homology of the muscles ; and whether they are solid or 
 hollow is merely a matter of detail. In later stages (Figs. 51 and 52) sections seem to 
 show that the peristomal depressions have deepened centrally so as to leave the inser- 
 tion of the septal muscles high up on the peripheral side. But here, again, before any 
 morphological conclusions can be drawn, account must be taken of the growth of the 
 perradial angles of the proboscis and of the effect of the contraction of the septal and 
 peristomal muscles. 
 
 Relation of Septa to Interradial Tentacles. According to Goette, the interradial 
 tentacles are always interseptal in origin. That is, two of these tentacles are produced as 
 diverticulae from each of the second pair of gastric pouches (ectoderrnal) . and their subse- 
 quent position in the planes of the septa is due to a secondary shifting. He finds 
 in this important evidence in favor of his theory of the close affinity between the 
 Scyphomedusae and the Anthozoa, for the tentacles of the latter are also invariably inter- 
 septal. Glaus, on the other hand, finds that the interradial tentacles of Aurelia and Coty- 
 lorhiza are variable in origin. According to his observations ('91 and '92) , an interradial 
 tentacle may be interseptal, that is, arise as a diverticulum of a single gastric pouch, the 
 endoderm growing out and pushing the ectoderm before it ; or it may arise in the plane of 
 a septum by the union of two endodermal diverticulae, one from each of the adjacent 
 pouches. He holds, therefore, that the origin of the tentacles cannot be used as evidence 
 to uphold Goette's theory. 
 
 My observations on Cassiopea are in perfect accord with those of Glaus. A number 
 of series of transverse serial sections made from young scyphistomas in the eight- and 
 sixteen-tentacle stages were studied carefully with the aid of camera sketches drawn on 
 transparent paper. By this means the relations of the parts could be determined accu- 
 rately ; and the results are embodied in the series of diagrams, Figs. H to L. In the 
 eight-tentacle stage, according to Goette, the gastric pouches in the long diameter, r r, 
 
CASSIOPEA XAMACHANA. 
 
 219 
 
 should each give rise to a single tentacle, while the pouches in the short diameter, r' r', 
 should each produce three. From a glance at Figs. H and J it will be seen that this is 
 not the case in Cassiopea. To 
 
 be sure, most of the tentacles at J-J I J 
 
 this stage are interseptal in 
 position, but the interradial ten- 
 tacles arise as often from pouch- 
 es in the long diameter, r r, as 
 from those in the short diame- 
 ter, r' r' ; and in both Figs. H 
 and I there is one interradial 
 tentacle that is distinctly septal 
 in position. The septa are still 
 complete, so that there can 
 hardly be any chance of a shift- 
 ing of position. In the sixteen- 
 tentacle stage, there is a ten- 
 tacle in the plane of each septum 
 (Figs. K and L) ; but here the 
 perforation of the septa has 
 commenced, and a shifting of 
 relative position is possible. 
 Even at this stage irregularities are common. For example, one of the septa in Fig. K is 
 placed asymmetrically with relation to the tentacles, and two tentacles are wanting in 
 Fig. L. 
 
 The Strobila, Development of the Rhopalia. When the scyphistoma has reached a 
 diameter of about two millimeters, there appear the first characters that are distinctive of 
 the strobila. The first noticeable change in this direction takes place at the bases of the 
 tentacles of the more erect series. This change may be regarded either as the outgrowth of 
 a conical lobe from the margin of the circumoral disc bearing the tentacle at its tip, or as 
 a conical widening of the basal portion of the tentacle. The former view is probably the 
 better. At about this time there appear in the tentacle, just beyond the apex of the cone 
 from which it springs, a few glistening white bodies. These are the so-called otoliths, and 
 mark the beginning of the formation of the rhopalium (Figs. 17 and 18). The tentacles 
 containing these will be called the rhopalial tentacles. 
 
 These concretions, or otoliths, increase in number until they form a conspic- 
 uous mass, while the basal cone begins to broaden laterally. This is now distinctly non- 
 
 Figs. H-L. Diagrams illustrating the space relations between the septa 
 and the tentacles, observed in five young scyphistomas of Cassiopea xama- 
 chana. r radii of the long diameter, r' radii of the short diameter. 
 
220 ROBERT PAYNE BIGELOW ON 
 
 contractile, and may be spoken of as a marginal lobe of the peristome (Figs. 19 and 
 20). In the specimen shown in Fig. 21 we see the first indication of stabilization. The 
 upper, expanded part of the calyx is separated from a conical, lower portion by a slight 
 groove. The marginal lobes have become semicircular in outline, and a slight elevation is 
 noticeable on the aboral side of each rhopalial tentacle immediately external to the mass 
 of concretions. The epithelium at this point is pigmented, and forms the first rudiment 
 of the eye (oc. Fig. 22) . Fig. 23 illustrates a more advanced stage, where the proximal 
 part of the tentacle is beginning to take on its final shape, and is separated by a pro- 
 nounced bend from the distal portion, which is still functional as a tentacle. 
 
 We come finally to a stage in which, while the long distal part of the tentacle retains 
 its characteristic structure and remains completely functional, the short proximal part 
 has become completely differentiated into a rhopalium. Fig. 54 is from a longitudinal 
 section of such a tentacle. The rhopalial part has assumed nearly its final shape. The 
 differentiation of its ectoderm into sensory epithelium, eye-spot, and layer of nerve fibres, 
 is complete. It has a lumen that extends outward to the solid chorda-like endoderm of the 
 distal part of the tentacle, and opens toward the centre into a gastric pocket. The endo- 
 dermal lining of the lumen is a columnar epithelium, the more distal cells being deeper 
 and containing the concretions. Compare Fig. 54 with Fig. 53, which, being interradial, 
 was certainly destined to be a rhopalial tentacle. 
 
 The growth of the marginal lobes, which were semicircular at the stage of Fig. 21, 
 has continued, and each lobe has now produced two secondary ones, one on each side of 
 the rhopalial tentacle. These are connected by a slight ridge that crosses the base of the 
 tentacle on its aboral side (h. Fig. 54) . The secondary lobes are the rhopalial lobes of 
 the margin of the umbrella (Flugellappen of German authors) , and the connecting ridge 
 is the hood (Deckplatte) that covers the rhopalium. These marginal structures may be 
 seen in Fig. 24, and this brings us to another stage in the development of the rhopalium, 
 the absorption of the distal part of the tentacle. 
 
 In the strobila shown in Fig. 24, the rhopalial tentacles have a very different 
 appearance from what we have seen before. They are shorter than the other tentacles, 
 and are much swollen at a point just beyond the eye-spot. The distal portion is begin- 
 ning to degenerate. This process, when once begun, proceeds rapidly. During the few 
 hours that were spent in making this drawing, the rhopalial tentacles were reduced in 
 length nearly one half. The eye-spots and concretions were conspicuous, and in each of 
 the former there was a slight cup-shaped depression. This is the earliest stage in which I 
 observed slight medusa-like movements of the ephyra disc. The tentacle at this stage is 
 in a process of degeneration for about fifteen hundredths of a millimeter outward from the 
 ocellus. In this area of degeneration ( t. Fig. 55) the endodermal cells are broken down, 
 
CASSIOPEA XAMACHANA. 221 
 
 the supporting membrane has disappeared, and the inner boundary of the ectoderm is 
 indistinct. The axial mass of this part of the tentacle is made up of loose particles of a 
 finely granular substance, in which may be seen many small and deeply stained nuclei. 
 There are also a number of green cells that apparently escaped into the central mass 
 when the supporting membrane broke down. There is evidently a free communication 
 between this mass of disintegrating material and the digestive cavity, through the 
 rhopalial canal. 
 
 The method by which the shortening of the tentacle is brought about would seem to 
 be as follows : The axial cells adjoining the cells that bear the concretions (Fig. 54) first 
 break down. Why they should do so, and at this particular time, I cannot say. This 
 disintegration proceeds centrifugally, and it is accompanied by a dissolution of the sup- 
 porting membrane. The ectodermal cells then either begin here and there to break 
 down while still in place, and the resulting debris is squeezed into the central cavity; or 
 else, the cells migrate, or are squeezed inward and then disintegrate. The continuity of 
 the remaining ectoderm is maintained, however. The products of degeneration prob- 
 ably pass through the rhopalial canal into the digestive tract. As this process continues, 
 the inward movement of the ectodermal cells is more rapid than their disintegration, so 
 that when the distal part of the tentacle is reduced to the size of the rhopalial part (Figs. 
 25 and 55), it is a solid mass of small cells with small nuclei that stain dark. Some of 
 these cells contain a large vacuole and have the nucleus pushed to one side. Scattered 
 among the small cells, there are a number of globular bodies as large as, or larger than, 
 the green cells, and completely filled with coarse granules that stain deeply with safranin; 
 no nucleus is visible in them. The ocellus has now become distinctly cup-shaped (oc. 
 Fig. 55). 
 
 At about this time the interrhopalial tentacles begin to be absorbed in their turn 
 (Fig. 25) . The umbrellar margin has in the mean time grown out beyond the insertion 
 of each interrhopalial tentacle, on its aboral side, into two lobes with a hood between 
 (Figs. 25 and 26) . This structure, although smaller, corresponds exactly to the rhopalial 
 lobes and hood, and is further evidence for the homology between the tentacles and the 
 rhopalia. The drawing reproduced in Fig. 25 was made between the hours of eleven 
 in the morning and two in the afternoon. At five o'clock of the same day the tentacles 
 had been reduced to one third the length shown in the figure, and the absorption of the 
 rhopalial tentacles was very nearly completed. 
 
 In the later stages of the absorption of the interrhopalial tentacles, the broken-down 
 material is evidently forced in some way into the radial canal. The rhopalium (Fig. 56) 
 is practically complete at this stage. The point (x) where the last trace of the tentacle 
 proper disappeared, is still distinguishable in sections by the presence of small cells with 
 indistinct cell walls, and by the absence of otoliths. 
 
222 ROBERT PAYNE BIGELOW ON 
 
 These observations, then, confirm those of Glaus ('83,) who, without going into the 
 details of development, maintained that the rhopalia are modified basal portions of the 
 tentacles of the scyphistoma; and they contradict Goette's statement that the rhopalia 
 are developed independently of the tentacles. 
 
 Other Phenomena of Stabilization. While the marginal structures are. undergoing 
 the metamorphosis that has just been described, important alterations are taking place in 
 the general shape of the body. The horizontal constriction first noticed in Fig. 21 has 
 deepened (Fig. 24), while the fold below it has heightened, and the upper portion has broad- 
 ened and flattened, until the condition shown in Fig. 26 is reached. At this final stage 
 the upper portion has all the characteristics of a free-swimming medusa (ephyrula), except 
 that it is attached by a slender aboral stem to the centre of a goblet-shaped basal polyp. 
 The four interradial depressions in the peristome of the earlier stages have become nearly 
 flattened out, all that remains of them being the hollows between the projecting radial 
 angles, or pillars, of the proboscis, which have now become very prominent. 
 
 At the stage of Fig. 21, there may be noticed on the proboscis eight patches of 
 thickened ectoderm containing many nettle cells. These nettle batteries are arranged 
 symmetrically, one on each side of each pillar of the proboscis. At a little later stage 
 (Fig. 24) the batteries have become invaginated, forming cup-shaped depressions, thickly 
 crowded with nettle cells in all stages of development. 
 
 During the time when the larva is being differentiated externally into an upper and 
 a lower portion, internal changes are taking place in the former, which result in the 
 disappearance of structures characteristic of the scyphistoma and the appearance of 
 others distinctive of the medusa. 
 
 The orifices in the gastric septa have become relatively larger (cs. Fig. 52 and re. 
 Fig. 57) until the septa are reduced to columnar pillars, columellae, connecting the upper 
 and lower walls of the body and pierced longitudinally by the septal muscles (c. Fig. 
 58) . The columellae are called by German authors "Septalknoten," but they are not 
 homologous with the so-called " Septalknoten," or areas of adhesion, in the Peromedusae. 
 The columellae of the Peromedusae are the walls of the large septal funnels where they 
 pass from the subumbrella to the exumbrella, and, according to Haeckel's figures, are 
 separated by the gonads from the areas of adhesion. 
 
 In the fully developed scyphistoma of Cassiopea, the septal muscles are solid 
 throughout their length, and there is no cavity corresponding to the septal funnels, 
 which, according to Goette, are well developed in Aurelia. But in the strobila there 
 does appear a slight depression extending a very short distance into the end of each 
 septal muscle. In Figs. 57 and 58, where this is well marked, much of the depression 
 may be due to the strongly contracted condition of the specimens; but other specimens 
 
CASSIOPKA XAMACHANA. 223 
 
 not so contracted show at least the deeper- part of the cavity, which therefore, may be 
 truly a vestige of the septa! funnel. 
 
 At an early stage of strobili/ation there may be noticed a short conical projection 
 from the central edge of each eolumella. It extends also around the sides. These pro- 
 jections are probably the rudiments of the first four gastric filaments, which are dis- 
 tinctly developed at the time when the ephyrula is set free (<jf, Fig. 58). 
 
 While the septa are shrinking to become the columellae, ridges appear opposite 
 each other on the upper and lower walls of the peripheral part of the digestive tract 
 between the bases of the tentacles. The epithelial membranes at the summits of oppo- 
 site ridges unite, and thus there is formed a series of lines of adhesion extending inward 
 from the periphery and dividing the space into a series of radial canals, each ending in 
 a tentacle. The two discs of mesogloea never fuse along these lines of adhesion, but the 
 endoderm remains between them as the endodermal lamella, or cathammal plate. At the 
 stage of Fig. 24 the lines of adhesion occupy about half the space from the margin to 
 the columellae. 
 
 The lower disc of the strobila remains simply an annular fold of the body wall until the 
 metamorphosis of the upper disc is nearly complete. The septa! muscles in this region 
 bend outward with the rest of the body wall (Fig. 57) . At length, however, the endoderm 
 grows out toward the periphery as four shallow pouches, leaving septa between them 
 which contain the longitudinal muscles. Very soon after this the septa are perforated so 
 as to allow a fusion of the endoderm at their upper angles (Fig. 58). In the last stage 
 of stabilization (Figs. 26 and 59) the longitudinal muscles may be traced from the 
 peristorae through the columellae and the mesogloea of the exuinbrella to the narrow 
 isthmus where the ephyrula disc joins the basal polyp. The latter has now a well- 
 developed peristome (Fig. 59), and the mesogloea in this region is very thin. Just in 
 the isthmus the muscles have disappeared, but they may be found again in the peristome 
 of the basal polyp and traced fora distance close under the epithelium to the edges of 
 the septa, where they bend abruptly downward, and continue through the septa into the 
 stem. 
 
 Although seldom visible in the living specimen, sections show that the basal polyp 
 at this sta-ge possesses eight short tenacles (Fig. 59). It has also an annular fold of the 
 ectoderm, closely surrounding the isthmus (Fig. 59 and p. Fig. 60) . This fold is the 
 rudiment of a new proboscis, which is without doubt entirely ectodermal in origin. But, 
 as Goette has pointed out, it does not follow from this that the lining of the proboscis is 
 ectodermal in scyphistomas developed from the egg. Pulsating contractions of the 
 umbrella are first noticed at the time when the rhopalial tentacles begin to be absorbed 
 (Fig. 24). They are then feeble and at long intervals. At the stage of Fig. 26 these 
 
224 ROBERT PAYNE BIGELOW ON 
 
 I 
 
 movements are rapid and violent. The rhythm is interrupted by few pauses, and these 
 are short. The result of these movements is that the thin wall of the isthmus is 
 ruptured, and the ephyrula is set free. 
 
 After this separation, the basal polyp has the appearance represented in Figs. 27 and 
 28. It is a scyphistoma with seventeen short tentacles and a rudimentary proboscis 
 (Figs. 61 and 62). The proboscis and the tentacles grow rapidly, so that in a few days 
 it is impossible to distinguish a regenerated basal polyp from a young scyphistoma in the 
 sixteen-tentacle stage, except that the former has a somewhat thicker stem. It may be 
 inferred from this complete regeneration of the basal polyp that it undergoes repeated 
 strobilization, as Glaus 1 has found to be the case in Aurelia. 
 
 The Ephyrula. The ephyrula of Cassiopea is very different in appearance from the 
 corresponding stage in ordinary scyphomedusae with eight rhopalia. Cotylorhiza has an 
 ephyrula resembling the same stage in the semostomatous medusae. Good figures of 
 this are given by du Plessis and Glaus, and there is a striking difference between these 
 figures and Figs. 29 and 30 in this paper, which are camera drawings of well-preserved 
 ephyrulas of Cassiopea, mounted in balsam. Fig. 29 represents a young Cassiopea that 
 has not long enjoyed a free existence. The general shape of the umbrella is like that of 
 the adult, and there is the same concavity in the centre of the exumbrella, while the 
 margin curves in the opposite direction, as in Fig. 64. The typical ephyrula of Aurelia 
 or Cotylorhiza has eight marginal arms with two lobes at the end of each, and between 
 each pair of lobes there is a rhopalium. In Cassiopea structures corresponding to these 
 arms are present to the number of sixteen, or often more. But these do not destroy the 
 general circular outline of the animal, for they are connected by thin areas on the 
 umbrella, alternating with an equal number of ridges, which at an earlier stage bore the 
 interrhopalial tentacles on their under sides. 
 
 We have, then, at this stage the marginal zone of the umbrella marked by a number 
 of short radial ridges separated by an equal number of thin areas. The ridges are in 
 line with the radial canals. At the peripheral end of each ridge the margin of the 
 umbrella is produced into two lobes, those adjoining the rhopalia being well marked, 
 the others small and inconspicuous (il. Fig. 30). 
 
 In Fig. 29 there are seventeen, and in Fig. 30, twenty-three, rhopalia. The latter 
 is an unusually large number, and it will be noticed that the number of marginal lobes 
 has not increased in proportion, so that irregularities of the margin occur in many places, 
 as described in the section on variations. 
 
 At this stage the rhophalia have come to lie, as in the adult, wholly within the margin 
 of the umbrella, and project from its subumbrellar surface. The interrhopalial tentacles 
 
 1 See foot-no te,_Claus ('92). 
 
CASSIOPEA XAMACIIANA. 225 
 
 have totally disappeared. The lines of adhesion separating the radial canals are faintly 
 visible as radiating lines of greater transparency. 
 
 The fcmr lips of the mouth are spread out into a cross-shaped figure, and one 
 may look directly through the lumen of the oesophagus into the stomach and see the 
 four gastric filaments (Figs. 29 and 30). Each one of the four lips is nearly square, and 
 from its two outer angles there are two grooves that extend obliquely inward until they 
 meet and form a V. The point of the V is in an angle of the oesophagus, along which 
 there is a groove that is continuous with the other two grooves, and that extends into 
 the stomach. On the interradial side of each of the eight labial grooves, there may be 
 seen a small roughly circular area that is less transparent than the rest. These areas are 
 the nettle batteries, first seen in the strobila. The margins of the lips are provided 
 with numerous small processes, the drgitella, which are arranged in a single continuous 
 series. 
 
 Fig. 63 is a section of an ephj^rula that has just become free. In this stage there is 
 still an opening through the aboral wall of the stomach, and one may see the last vestige 
 of the connection between the columella and the exumbrella, which contains also the 
 degenerating remnants of the septal muscle. 
 
 At a little later stage, when the opening in the roof of the stomach has closed, 
 both the septal muscles and the septal funnels totally disappear. Sometimes one, some- 
 times the other, is the first to vanish. 
 
 The Later Stages. The later stages in the development of Cassiopea will be 
 treated very briefly. While the umbrella remains at first unchanged, the metamor- 
 phosis of the mouth parts is inaugurated by the growth of the two outer angles of each 
 of the more or less quadrate lips, so that they [are soon drawn out into extended lobes 
 (Fig. 31). At the same time the pillars of the proboscis thicken, and the mesogloea is 
 continued outward along each of these lobes as a midrib. We have then eight oral 
 arms, each with a longitudinal groove, supported by a midrib, and fringed with digi- 
 tella, arms very similar to those characteristic of the genus Aurosa Haeckel ('79) . But 
 it is only the mouth parts of Cassiopea that may be said to pass ^through an Aurosa stage, 
 for the comparison cannot, at this time at least, be carried to the other organs. 
 
 Glaus has described ('83) some of the principal stages in the metamorphosis of Pilema 
 (Rhizostoma) and Cotylorhi/a. He regards the formation of the eight oral arms as a dif- 
 ferent process in these forms from what occurs in Aurosa. But it appears to be merely the 
 same thing expressed differently. 
 
 In the next stage we find two oral funnels, or oscula, and a small vesicle developed at 
 the tip of each oral arm. The other portions of the arm are still open and fringed with 
 digitella, as before, but the outline is no longer a regular curve, for there are folds in the 
 
226 ROBERT PAYNE 15KJELOW ON 
 
 margin. The deepest folds are the most distal, and they become progressively more 
 shallow toward the base of the arm. The central mouth is still widely open. The subgeni- 
 tal cavities are well developed at this stage. Figs. 64, 65, and 66 show how the oral disc 
 is formed, and how the subgcnitsil cavities are produced by the great increase in thickness 
 of the mesogloea at the pillars of the proboscis and the bases of the oral arms. By the 
 growth of these structures, the subgenital cavities are necessarily produced. The only 
 special adaptations are the subsequent growth and folding of the aboral wall and the 
 narrowing of the orifice. 
 
 The marginal lobes of the umbrella now begin to broaden, and thus approach the 
 adult condition, but there is only a single "vellar" lobe between two rhopalial ones. 
 
 At a little later stage, when there are three oral funnels at the tips of the arms 
 (Fig. 33), the re-entrant angles between the pillars of the proboscis have grown inward, 
 met at the centre, and fused. In this Avay the lumen of the oesophagus is divided 
 into four tubes (Fig. 32) , representing the grooves that were present in its angles in the 
 earlier stages. In the figure the fusion at the centre has gone so far as to involve the 
 edges of the lips, and the labial grooves of the different pairs of arms are not in open 
 communication, but a short cross-shaped tube connects them at the centre, and the oral 
 disc is now completed. 
 
 It is interesting to note that Clans has found a stage both in Pilema and in Coty- 
 
 
 
 lorhiza that, while showing the characteristic family differences, has also a certain 
 resemblance to this stage in Cassiopea. In all three the walls of the proboscis have fused 
 so as to divide its lumen into four tubes, and the formation of oscula has begun at the tips 
 of the arms in such a way that we have on each arm three oscula with a vesicle in the 
 angles between them. The occurrence of this stage in the ontogeny of three so distinctly 
 separated families must have some morphological significance, and we may regard these 
 eight primary vesicles as homologous in the three groups. 
 
 The mode of formation of the oral funnels becomes evident at this stage. They are 
 not formed in Cassiopea simply by a series of fusions of the lips along the line of the 
 labial groove, as Hamann ('8l) states to be the case in Cotylorhiza. It is more like the 
 process in Pilema, as described by Clans. Each of the primary funnels is represented at 
 first by one of the folds in the margin of the lips referred to above (Fig. 33) . The 
 fold deepens, and its edges are brought together on the ventral side and fuse, leaving an 
 opening at the apex of the fold, the osculum. At the same time the labial groove in 
 this region is converted into a canal by the fusion of the lips on its two sides. After 
 the fusion all trace of what has occurred quickly disappears. 
 
 Witli, the division of the oesophagus into four tubes, and the completion of the oral 
 disc, our larva comes to be distinctly a rhizostomatous medusa. Further development of 
 
CASSIOPEA XAMACUANA. 227 
 
 the mouth parts consists in the continued division of the labial, or brachial, grooves into 
 oral funnels and brachial canal, together with the development of oral vesicles. By the 
 time two or three vesicles have been formed on the end of each arm, a vesicle appears in 
 the centre of the oral disc. Except for this interruption, the development of the mouth 
 parts proceeds regularly in a centripetal direction. The funnels and vesicles are formed 
 lirst at the tips of the arms, and then one after another in regular succession toward the 
 centre. Each of these primary funnels is the rudiment of one of the primary branches of 
 the arm. When the process of forming funnels has reached about half the length of the 
 arm, the distal funnels begin to subdivide. By this subdivision of the primary funnels 
 new ones are produced, of which some are the rudiments of secondary branches ; these sub- 
 divide again, and so on, as long as growth continues. The subdivision is not dichotomous, 
 but takes place in such a way as to produce alternate branches. The formation of a 
 vesicle takes place at this stage in some way at about- the time of the completion of the 
 adjoining funnel. I have not been able to determine whether the vesicle is a funnel with 
 (lie orifice closed, as Ilamanu claims it to be, or whether it is an evagination from the 
 pedicle of a funnel, as at first it seemed to me to be, and as Glaus thinks it probably is. 
 
 According to Haeekel ('79), the genus Archirhiza represents a form that was the 
 ancestor of all the rhizostomatous medusae. Of this genus there are two known species, 
 A. primordiafis Haeekel, and A. miroxa Haeekel. They agree in having four subgenital 
 cavities and eight simple unbranched arms that are provided with a single zig-zag row of 
 closely set oral funnels, and are devoid of other appendages. Hamann says that a stage 
 representing this condition is a feature of the ontogeny of rhizostomatous medusae. From 
 what has been said it is evident that we have no such stage in the development of Cassi- 
 opea xamachana, for while the labial groove is still open in the proximal half of the oral 
 arm, in its distal half the vericles are formed, and branches are in the process of 
 formation. 
 
 The outline of the umbrellar margin has not changed essentially since the last stage. 
 The areas of adhesion have become much wider than the radial canals they separate, and 
 in them there has appeared a network of anastomosing canals, while the gastric filaments 
 have become numerous. 
 
 We have now followed the larva of our Cassiopea from its first appearance as a bud 
 to a point where, with the exception of the gonads, all the organs of the adult are out- 
 lined. Here we must take leave of it. 
 
228 ROBERT PAYNE BIGELOW ON 
 
 SUMMARY AND CONCLUSIONS. 
 
 Cassiopea and Polyclonia are genera of rhizostomatous medusae peculiarly modified in 
 adaptation to a sedentary mode of life in shallow water among the mangroves bordering 
 tropical seas. A comparison of specimens of Polyclonia frondosa Ag. with Cassiopea 
 xamachana shows that these two forms are specifically distinct, although in general 
 appearance they are very similar and they have the same geographical range and 
 habitat. 
 
 C. xamachana is remarkable for its variability. This is especially shown in the 
 appendages to the mouth parts and in the structures at the margin of the umbrella. It 
 will be noticed that the most frequent number of rhopalia, in the twenty-seven specimens 
 examined, was sixteen, which is the typical number for the genus. But the variations are 
 hot arranged symmetrically on the two sides of this mode, for specimens having a 
 greater number of rhopalia are more than twice as many as those having less. The 
 species shows a strong tendency toward duplication of the rhopalia and associated struc- 
 tures of the umbrella ; and at the same time the symmetrical relations of the parts tend 
 to be preserved. The great majority of scyphomedusae have only eight rhopalia, and in 
 Cassiopea with its sixteen rhopalia we have a beautiful illustration of Darwin's law that 
 " A part developed in any species in an extraordinary degree or manner, in comparison 
 with the same part in allied species, tends to be highly variable." Study of the color 
 markings and measurements of the mouth parts indicates the division of the species into 
 three varieties; and it was in one of these, var. A, that the duplication of marginal organs 
 was especially prevalent. 
 
 The color of both larvae and adults is due to a great extent to the presence in the 
 mesogloea of minute symbiotic algae. That these are plant cells was demonstrated by 
 micro-chemical tests. Their presence undoubtedly enables the medusae to live in water 
 that would be too poor in oxygen for most marine animals. 
 
 The search for developing eggs proved unsuccessful, but scyphistoma larvae were 
 abundant, and it was found that they were multiplying rapidly by budding. 
 
 The bud arises as an evagination of the body wall of the scyphistoma. There is no 
 evidence of any special gemminal epithelium. The bud, when set free, differs from a 
 planula chiefly in the possession of a well-defined mesogloea and four septal muscles. The 
 septal muscles are shown to be formed as branches of the two adjacent septal muscles of 
 the parent. The mouth of the young scyphistoma is formed by a minute perforation at, 
 the former point of attachment, while the distal end of the bud becomes the stem. This 
 remarkable orientation agrees with what Goette and Clans have found in Cotylorhita, In 
 
CASSIOPEA XAMACHANA. 229 
 
 the formation of the mouth there is no evidence of any invagination of ectoderm Ap- 
 parently the oesophagus, as well as the gastric pouches, is lined with endoderm. On 
 the other hand, the oesophagus of the lower disc of the strobila is formed wholly of 
 ectoderm. 
 
 The four radial tentacles are formed simultaneously, and the four interradial ones 
 appear at the same time or slightly later. These are followed by eight adradinl tentacles 
 and sixteen more are added a little later, making thirty-two in all. It was found that the 
 rudiments of the interradial tentacles are not at all constant in position with relation 
 to the septa. Some were septal, others were interseptal, sometimes on one side of the 
 septum, sometimes on the other, thus agreeing with the observations of Glaus on Aurelia 
 and Cotylorhiza. 
 
 The four gastric pouches are formed at the same time by the ingrowth of the septa. 
 They are soon brought into communication at the periphery by the perforation of the 
 septa, which become reduced to columellae surrounding the longitudinal muscles. 
 
 Contrary to Goette's opinion, it may be staled positively that the rhopalia are differ- 
 entiated in the bases of alternate tentacles. After the rhopalium is fully developed, the 
 distal part of the tentacle undergoes degeneration and is absorbed. The development was 
 traced for the first time through all its stages, and the opinions of Agassiz, Claus, and 
 Lendenfeld are fully confirmed. 
 
 The scyphomedusae are the only coelente rates, which possess four longitudinal 
 muscles of ectodermal origin completely imbedded in the mesogloea between the points of 
 insertion. The buds of Cassiopea have this distinctively medusoid characteristic long 
 before they are detached. Moreover, the methods by which the mouth and the gastric 
 pouches are formed differ entirely from what is said to take place in larvae that pass 
 through an anthozoan stage. Therefore, whatever may be true of the larvae derived from 
 eggs, this stage is certainly omitted in larvae produced by budding. 
 
 The first step toward the formation of the free-swimming medusa is the perforation 
 of the gastric septa which takes place in the young scyphistoma before it is fully 
 developed. Then follows a period of growth and reproduction by budding, and further 
 metamorphosis begins finally with the process of strobilization. Besides the differentia- 
 tion of the sense organs and the development of the marginal lobes of the umbrella, the 
 most important events are the development of the angles of the mouth into quadrate 
 lobes and the fusion of the two layers of endoderm along certain areas of adhesion so as 
 to divide the periphery of the digestive tract into a series of radial canals. Only one 
 medusa is formed ; but, separated from this by a constriction, is a small basal segment 
 which, a short time before the medusa becomes free, begins to develop gastric pouches, 
 tentacles, and a proboscis. This becomes eventually a perfect scyphistoma, and after a 
 period of growth probably undergoes stabilization again. 
 
230 ROBERT PAYNE BIGELOW ON 
 
 There has been considerable discussion in regard to the nature of stabilization; the 
 question being whether the medusa is to be regarded as a metamorphosed scyphistoma, 
 or as derived from the scyphistoma by a process of budding. In the monodiscous strobila 
 of Cassiopea we have clearly a metamorphosis. The form of the medusa is the result of a 
 series of changes which begin very early and involve all the essential organs of the scy- 
 phistoma. The portion not involved in these changes merely serves as a mechanical sup- 
 port. That this part is separated off and regenerates the lost parts, instead of being 
 absorbed, may be regarded as merely an incidental fact. 
 
 If there be any question of budding it refers to this basal segment. And this suggests 
 a striking analogy between the basal polyp and the peculiar planula-like buds. In the 
 first place they have the same orientation relative to the upper disc. In both, the distal 
 end forms the stem and the proximal end forms the mouth. In the second place, they 
 have essentially the same structure. Each one consists of a simple sac with a wall made 
 up of three layers, ectoderm, mesogloea and endoderm, and each is provided with four longi- 
 tudinal muscles imbedded in the mesogfoea. What differences appear in the subsequent 
 development, may be attributed to the different ways in which the two become separated 
 from the disc and to the greater size of the longitudinal muscles in the basal polyp. The 
 production of supernumerary tentacles, rhopalia, and marginal lobes, is common in this 
 species. Why may we not regard the buds as supernumerary basal polyps, and their 
 subsequent development as a process of regeneration preserved and modified by natural 
 selection for its obvious advantage? 
 
 The ephyrula of Cassiopea has the same number of rhopalia as the adult, and differs 
 in shape from the corresponding stage of ordinary scyphomedusae with eight parameres. 
 
 The most important event in the later stages is the metamorphosis of the mouth 
 parts. The angles of the four quadrate lips become extended to form eight oral arms 
 somewhat similar to those found in the adult Aurosa. There is no Archirhiza stage, but 
 there follows a stage with the oesophagus divided into four tubes, and with three oscula 
 and an oral vesicle on each arm. A similar stage has been found in Pilema and Coty- 
 lorhiza, and it may have some phylogenetic significance. 
 
 The studies of numerous investigators upon the Ascidians have demonstrated that a 
 knowledge of the gamogenetic development of an animal will not always enable one to 
 predict how the organs will be formed in the agamogenetic process. So it may be 
 objected that the results set forth in this paper do not afford a valid basis for the criticism 
 of work done by others on larvae developed from the egg. On the other hand, the eight- 
 tentacle stage of the bud larva of Cassiopea is so like the same stage of the sexually pro- 
 duced larva of its near relative Polyclonia that it would be impossible to tell them apart, 
 and, in the absence of any evidence to the contrary, there seems to be no necessary reason 
 
CASSIOPEA XAMACHANA. 231 
 
 for supposing that their later history is different. At any rate, we have here the first 
 fairly complete history of the development of a scyphomedusa from the bud; and when 
 the sexual development of Cassiopea xamachana or an allied species is studied, this 
 memoir will serve as a means of comparison, and will make it possible to determine 
 whether or not the two modes of ontogeny are alike. 
 
 LITERATURE. 
 
 Agassiz, A. 
 
 '65. North American Acalephae. Illustrated catalogue of the Museum of comp. zool. at Harvard College. No. 2, 1865, 
 
 p. 41. 
 
 '81. Polyclonia frondosa. Nature, vol. 24, 1881, p. 509. 
 Agassiz, A., & Mayer, A. G. 
 
 '99. Acalephs from the Fiji Islands. Bull. mus. comp. zool., vol. 32, no. 9, 1899. (Description of Cansiopea ndrnsia.) 
 Agassiz, L. 
 
 '60. Contributions to the natural history of the United States of America. Vols. 3 and 4. Boston, 1860. 
 Archer, H. 
 
 '81. Medusae. Nature, vol. 24, 1881, p. 307. 
 Berger, E. W. 
 
 1900. Physiology and histology of the Cuboinedusae, including Dr. F. S. Conant's notes on physiology. Mem. biol. 
 
 lab. Johns Hopkins Univ. vol. 4, no. 4. 
 Bigelow, R. P. ^ 
 
 '90. The marginal sense organs in the Pelagidae. Johns Hopkins Univ. oirc., vol. 9, 1890, no. 80, p.5. 
 
 '92a. On reproduction by building in the Discomedusae. J. H. U. circ., vol. 11, 1892, no. 97, p. 71. 
 
 '92b. On the development of the marginal sense organs of a rhizostomatons medusa. J. H. U. circ., vol. 11, 1892. 
 
 no. 97, p. 84. 
 
 '92c. On a new species of Cassiopea from Jamaica. Zool. Anz., Jahrg. 15, 1892, no. 393, pp. 212-214. 
 '93. Some observations on Polyclonia frondosa. J. H. U. circ., vol. 12, 1893, no. 106, p. 106. 
 Brandt, J. F. 
 
 '38. Ausfiirliche Beschreibung der von C. H. Martens auf seiner Weltumsegelung beobachteteii Schirmquallen. Mem. 
 
 Acad. imp. sci. St. Petersbourg, sci. math. phys. et nat., (6) vol. 4 (pt. 2, sci. nat., vol. 2), 1838, pp. 394-399. 
 Brooks, W. K. 
 
 '86. The life history of Hydromedusae, a discussion of the origin of medusae and the significance of metagenesis, 
 
 Mem. Boston soc. nat. hist., vol. 3, no. 12, 1886 ; also Mem. biol. lab. Johns Hopkins Univ., vol. 1. 
 Claus, C. 
 
 '77. Studien tiber die Polypen und Quallen der Adria. Denkschr. d. math.-naturw. Classe d. k. Acad. d. Wissen- 
 
 schaften, Wien, Bd. 38, 1877. 
 
 '81. Ueber einige bislang noch unbekannte Larvenstadien von Rhizostoma. Zool. Anz., 1881, No. 76, p. 79. 
 '83. Uutersuchvmgen fiber die Organisation und Entwicklung der Medusen. Prag and Leipzig, 1883, 96 pp., 20 pis. 
 '84. Die Ephyren von Cotylorhiza und Rhizostoma. Arb. zool. Inst. Wien, vol. 5, 1884, p. 169. 
 "90. Ueber die Entwicklung des Scyphostoma von Cotylorhiza, Aurelia, und Chrysaora, I. Arb. zool. Inst., Wien, 
 
 vol 9, 1890, p. 29. 
 
 "92. Ueber die Entwicklung des Scyphostoma von Cotylorhiza, Aurelia, und Chrysaora, sowie iiber die systematise-lie 
 Stellung der Scyphomedusen, II, Arb. a. d. zool. Inst. $. Univ. Wien, vol. 10, 1892, pp. 1-70. 
 
232 ROBERT PAYNE BIGELOW ON 
 
 du Plessis, G. 
 
 '81. Remarques sur les metamorphoses de la Cassiope'e bourbounieune. Bull. soc. vaudois, Lausanne, ser. 2, vol. 17, 
 
 1881, p. 633. 
 Fewkes, J. W. 
 
 '82. Notes on acalephs from the Tortugas, with description of new genera and species. Bull. mus. conip. Zool., vol. 9, 
 
 no. 7, 1882. 
 Fischer, P. 
 
 '88. Note sur des scyphistomes de mSduse acraspede. Bull. soc. zool. de France, vol. 13, 1888, p. 96. 
 Forskal, P. 
 
 1775. Deseriptiones animalium .... quae in itinere oriental! observavit. Hauniae, Moller, 1775, p. 107. 
 
 1776. Icones rerum naturaliuin, quas in itiuere oriental! depingi curavit. Hauniae, 1776, pi. 31. 
 Frautzius, A. v. 
 
 '53. Ueber die Jungeii der Cephea (Cotylorhiza.). Zeitschr. f. wiss. Zool., Bd. 4, 1853, p. 118. 
 Goette, A. 
 
 '87. Entwicklungsgeschichte des Aurelia aurita und Cotylorhiza tuberculata. Hamburg and Leipzig, 1887. 
 
 '91. Claus und die Entwicklung der Scyphomedusen. Leipzig, 1891. 
 
 '93. Vergleichenden Entwicklungsgeschichte von Pelagia noctiluca P6r. Zeitschr. f. wiss. Zool. Bd. 55, 1893, pp. 645- 
 
 695. [Die Larven von Cotylorhiza tuberculata L., pp. 645-659.] 
 Gray, J. E. 
 
 '69. Habits of the Medusae. Annals and mag. nat. hist., ser. 4, vol. 4, 1869, p. 296. 
 Guppy, H. B. 
 
 '82. Habits of Scyphomedusae. Nature, vol. 27, 1882, p. 31. 
 Haacke, W. 
 
 '85. Pseudorhiza Haeckelii spec, nov., der Endspross des Discomedusenstammes. Biol. Ceutralb., vol. 4, 1885, p. 291. 
 Haeckel, E. 
 
 '69. Crambfissiden. Zeitschr. f. wiss. Zool., vol. 19, 1869, p. 509. 
 
 '79. Das System der Medusen. Jena, 1879. 
 
 '81a. Report on the deep sea medusae. Challenger reports, zool., vol. 4, 1881. 
 
 '81b. Metagenesis and Hypogeuesis von Aurelia. Jena, 1881. 
 Hamann, O. 
 
 '81. Die Mundarme der Rhizostomen und ihre Anhangsorgane. Jenaische Zeitschr. f. Naturw., vol. 16, 1881, p. 243. 
 Hertwig, O. & R. 
 
 '78. Das Nervensystem und die Sinnesorgane der Medusen. Leipzig, 1878. 
 
 '79. Die Actinien. Jena, 1879. 
 Hesse, R. 
 
 
 
 '95. Ueber das Nervensystem und die Sinuesorgane von Rhizostoma cuvieri. Zeitschr. f. wiss. Zool., vol. 60, 1895, 
 
 p. 411. 
 Hyde, Ida H. 
 
 '94. Entwicklungsgeschichte eiuiger Scyphomedusen. Zeitschr. f. wiss. Zool., vol. 58, 1894, p. 531-565. 
 Keller, C. 
 
 '83. Untersuchungen fiber neue Medusen aus dem Rothen Meere. Zeitschr. f. wiss. Zool., vol. 38, 1883, p. 621. 
 Lacaze-Duthiers, H. de. 
 
 '93. Scyphistome. Archives de zool. expfcr., ser. 3, vol. 1, 1893, notes et revues, p. xxx. 
 Lamarck, J. B. de 
 
 '37. Histoire naturelle des animaux sans vertfibres. Ed 3. Paris, 1837, vol. 1, p. 457. 
 Lang, Albert. 
 
 '92. Ueber die Knospung bei Hydra und einigen Hydropolypen. Zeitschr. f. wiss. Zool., vol. 54, pp. 363-385. 
 Lendenfeld, R. v. 
 
 '82. Ueber eine Uebergangsform zwischen Semostomen und Rhizostomeu (Pseudorhiza). Zool. Anz., Jahrg. 5, 1882, 
 p. 380. 
 
CASSIOPEA XAMACHANA. 
 
 233 
 
 '84. Znr Metamorphose der Rhizostomen. Zool. Anz., Jahrg. 7, 1884, p. 429. 
 
 '88. Die australischen rhizostninen Medusen. Zeitsclir. f. wi.sg. Zool., vol. 47, 1888, p. 201. 
 McMurrich, J. P. 
 
 '91. The Development of Cyanea arctica. Amer. nat., vol. 25, 1891, p. 287. 
 Metschnikoff, E. 
 
 '86. Embryologische Studien an Medusen. Wien, 1880. 
 Milne-Edwards, H. 
 
 '49. Les zoophytes. Cuvier, Regne animal illustrfi. Vol. 10, 1849, pi. 51. 
 Reid, J. 
 
 '48. Observations on the development of the medusae. Annals and mag. nat. hist., ser. 2, vol. 1, 1848, p. 25. 
 Sars, M. 
 
 '41. Ueber die Entwicklung der Medusa aureta und Cyanea capillata. Arch. f. Naturg., vol. 7, 1841, p. 9. 
 Schewiakoff, W. 
 
 '89. Beitrage zur Kenntnis der Acalephenauges. Morph. Jahrb., vol. 15, 1889, p. 25. 
 Schneider, A. 
 
 '70. Zur Entwicklimgsgesehichte der Aurelia aurita. Arch, f. mik. Anat. vol. 6, 1870, p. 363. 
 Schultze, L. S. 
 
 '98. Rhizostomen von Ternate. Abh. senckenb. naturf. Ges., vol. 24, 1898, p. 153. [Occurrence of Cassiopea, sp.?] 
 Smith, Frank. 
 
 '91. The gastrulation of Aurelia flavidula P^r. & Les. Bull. mus. comp. zool., vol. 22, no. 2, 1891. 
 Tilesins, W. G. v. 
 
 '29. Zur Naturgeschichte der Medusen. Nova Acta Physico-Medica, N. C., vol. 15, 1829, p. 266. 
 Vanhoffen, E. 
 
 '88. Untersuchungen iiber semaeostome und rhizostome Medusen. Leuckart & Chun's Biblioth. Zool., Heft 3, 1888. 
 
 EXPLANATION OF PLATES. 
 
 All the figures from I to 28, and Figs. 34 and 35, are freehand drawings made from the living animals. Figs. 29 to 
 33 are from well-preserved specimens mounted in balsam, and were outlined with the camera lucida. The remaining figures, 
 except Fig. 37, are camera-lncida drawings of microtome sections. All the figures are reduced uniformly to slightly less 
 than one half the diameter of the original drawings. 
 
 LETTERING COMMON TO ALL THE FIGURES. 
 
 b. bud. 
 
 c. columella. 
 
 c d. circum-oral disc, or peristome. 
 
 cs. circular sinus. 
 
 ex. calyx. 
 
 d. digitellum. 
 
 ect. ectoderm. 
 
 e 1. endodermal lamella, or cathammal plate. 
 
 end. endoderm. 
 
 e u. exumbrella. 
 
 g. stomach. 
 
 g f . gastric filament. 
 
 g p. gastric pouch. 
 
 h. hood. 
 
 i 1. interrhopalial lobe. 
 
 i t. interrhopalial tentacle. 
 
 1 g. labial groove. 
 
 m. mouth. 
 
 mes. mesogloea, or supporting membrane. 
 
 n f. nerve fibres. 
 
 o a. oral arm. 
 
 oc. ocellus. 
 
 o d. oral disc. 
 
 oe. oesophagus. 
 
234 
 
 ROBERT PAYNE BIGELOW ON 
 
 oe. t. oesophageal tube, or canal. 
 
 os. osmium. 
 
 ot. rhopalial concretion (otulitli). 
 
 p. proboscis. 
 
 p p. pillar of the proboscis. 
 
 r c. radial canal. 
 
 rh. rhopalium. 
 
 rh. c. rhopalial canal. 
 
 rh. t. rhopalial tentacle. 
 
 s. stem. 
 
 s e. sensory epithelium. 
 
 sep. septum. 
 
 s f. septal funnel. 
 
 s g. subgenital cavity. 
 
 s in. septal muscle. 
 
 s u. subumbrella. 
 
 t. tentacle. 
 
 v. vesicle. 
 
 za. brownish green cells, symbiotic algae. 
 
 PLATE 31. 
 
 Fig. 1. Portion of the calyx and stem of a scyphistoma with a fully developed bud (ft) attached. A, the outline of the 
 same bud when contracted. 
 
 Fig. 2. Similar to the preceding, except for the formation of a second bud (ft') which bears the older one (ft) upon its 
 apex. 
 
 Fig. 3. The form of the plamila-like bud during the first tw,> days after becoming free. A, B, and C, are the successive 
 changes in shape observed in one specimen during a few minutes. The arrows show the direction in which it swims. 
 
 Fig. 4. Larva of probably the third day. A, lateral aspect; B, oral aspect. 
 
 Fig. 5. A larva of about the same age, 48 hours or over. 
 
 Fig. 6. Another larva of 48 hours or over. 
 
 Fig. 7. Larva of the fourth day.. 
 
 Fig. 8. Free scyphistoma of the fifth day, with rudiments of four tentacles. The arrows show the direction of progres- 
 sion and rotation. 
 
 Fig. 0. A scyphistoma of about the same age, with the rudiments of eight tentacles. 
 
 Fig. 10. Oral aspect of a similar larva, perhaps somewhat younger. 
 
 Fig. 11. A scyphistoma a little mare advanced, probably in, the fifth day. 
 
 Fig. 12. A still more advanced scyphistoma of the fifth day. The four tentacles first formed are much longer than the 
 other four. 
 
 Fig. 13. Scyphistoma of the sixth day, attached, and with eight tentacles. 
 
 Fig. 14. Scyphistoma with rudiments of the second set of eight tentacles. Two tentacles of the first series are bifur- 
 cated. 
 
 Fig. 15. Scyphistoma with sixteen tentacles fully developed, in tile attitude of feeding. 
 
 Fig. 16. Oral aspect of a similar specimen. 
 
 PLATE 32. 
 
 Fig. 17. Scyphistoma showing first traces of rhopalial structure. 
 
 Fig. 18. A small portion of the margin more highly magnified. 
 
 Fig. 19. Scyphistoma at a slightly older stage. 
 
 Fig. 20. Small part of the margin of a similar larva. 
 
 Fig. 21. An early stage in strobilization. 
 
 Fig. 22. A rhopalial tentacle of the same specimen seen from the side. 
 
 Fig. 2.3. An older rhopalial tentacle. 
 
 Fig. 24. Strobila in which the rhopalial tentacles have begun to degenerate. 
 
CASSIOPEA XAMACHANA. 235 
 
 PLATE 33. 
 
 Kite. 26. Strobila, in whicli the degeneration of the rhopalial tentacles is nearly completed, and the interrhopalial 
 tentacles have begun to degenerate. 
 
 Fiji. '26. A complete strobila. The basal polyp bears a bud which broke off and swam away while the drawing was 
 being made. The ephyrula was detached during the following night. The rhopalia are visible through the umbrella. 
 At y, is a pair of twin rhopalia ; compare y, Fig. 30. 
 
 Fig. 27. Tue basal polyp of the same specimen, a few hours after the separation of the ephyrula. 
 
 Fig. 28. Optical section of the same. 
 
 Fig. 29. An ephyrula recently set free. Oral aspect. The gastric filaments are visible through the mouth, x 31. 
 
 Fig. 30. A specimen of about the same age, showing variations of the margin at u, w, x, y and z. X 31. 
 
 PLATE 34. 
 
 Fig. 31. Mouth parts of a young medusa in the Aurosa stage. The gastric filaments may be seen through the central 
 mouth opening. X 33. 
 
 Fig. 32. Oral disc of an older specimen. The oesophageal tubes appear as light areas, one at the junction of each pair 
 of labial grooves. 
 
 Fig. 33. One of the oral arms from the same specimen as Fig. 32. 
 
 Fig. 34. Floor of the stomach and the oral arms of an adult viewed from the aboral side. The roof of one subgenital 
 cavity is removed, and a threat! is represented as passing through the external orifice into this cavity, at x. The ultimate 
 branches are represented on only one of the oral arms. 
 
 Fig. 35. Portion of the aboral surface of an adult. About half natural size. 
 
 PLATE 35. 
 
 Fig. 36. Section of a young bud. X Zeiss DD + oc. 2.' 
 
 Fig. 37. Diagram to show the branching of the septal muscles, SHI,, am,, sm 3 and xm t , and the connections of the 
 septal muscles of the bud, sm',, sm' n , and ?'.,. Reconstructed from the series of sections of which Fig. 36 is one. 
 
 Fig. 38. Section through the distal apex of an older bud, showing the attachment of a septal muscle to the ectodennal 
 epithelium. X Zeiss II + oc. 2. 
 
 Fig. 39. Longitudinal section of a planula-like larva. D was the distal, and P the proximal, end of the bud while 
 attached. X Zeiss DD + oc. 2, dt. ICO. 
 
 Fig. 40. Longitudinal section through the posterior end of a swimming larva, in which changes preparatory to the 
 formation of the mouth are taking place. X B & L i + Zeiss oc. 2. 
 
 Fig. 41. Similar section of a slightly older larva, showing the mo.uth as a small opening not exceeding in width the 
 thickness of the section. X B & L J + Zeiss oc. 2, dt. 160. 
 
 Fig. 42. Adradial section of a scyphistoma a little older than Fig. 9 (5th day). X Zeiss DD + oc. 2. 
 
 Fig. 43. Obliquely transverse section of a specimen of the same age, showing the greatest width of one septum. X B 
 & L J + Zeiss oc. 2, dt. 160. 
 
 Fig. 44. A tangential section of an older larva, showing the connection of a septal muscle with the circum-oral disc. 
 X Zeiss H + oc. 2. 
 
 PLATE 36. 
 
 Figs. 45 to 47 are consecutive transverse sections of one individual. Fig. 45 shows the continuity between the endoderm 
 of adjacent gastric pouches at the base of an interradial tentacle. Fig. 47 is lower, and here the gelatinous septum com- 
 pletely separates the two pouches. X Zeiss H + oc. 2. 
 
 1 Unless otherwise noted, the microscope was used with the draw tube not drawn out. Length of tube (dt.) = 1ST mm. 
 
-236 ROBERT PAYNE BIGELOW ON CASSIOPEA XAMACHANA. 
 
 Figs. 48 and 49 are from the same series. Fig. 48 is the second section below Fig. 47. It just clears the oesophagus. 
 Fig. 49 is through the upper part of the stem. X Zeiss DD -f oc. 2. 
 
 Fig. 50. Longitudinal section of a scyphistoma with sixteen tentacles, probably a little younger than Fig. 15. X Zeiss. 
 DD + oc. 2, dt. 195. 
 
 Fig. 61. An obliquely transverse section of a fully developed scyphistoma, showing the relations of the septal muscles 
 to the depressions in the circumoral disc. The mesogloea is shaded. X Zeiss B + oc. 2, dt. ICO. 
 
 Fig. 52. Part of an interradial section from a scyphistoma a little older than the last. Owing to a slight obliquity of 
 the section, the full extent of the circular sinus at the base of the tentacle is not shown. It extends to the point marked x. 
 X Zeiss C + oc. 2. 
 
 PLATE 37. 
 
 Figs. 63 to 56 illustrate the development of the rhopalia. 
 
 Fig. 53. Median section of the interradial tentacle shown in Fig. 52 ; x marks a corresponding point in the two sections 
 X Zeiss H + oc. 2. 
 
 Fig. 54. A radial section from the base of a rhopalial tentacle somewhat older than Fig. 23. X Zeiss H + oc. 2. 
 
 Fig. 55. Radial section of a rhopalium in the stage of Fig. 25. x Zeiss H -}- oc. 2. 
 
 Fig. 56. Radial section of a rhopalium in about the stage of Fig. 26. X Zeiss H + oc. 2. 
 
 Fig. 57. Radial section showing the course of a septal muscle in a strobila, at the stage of Fig. 24. X ZeLss DD + oc. 2. 
 
 Fig. 58. A similar section from a specimen a little older than Fig. 25 ; x, point of separation between the two discs. 
 X Zeiss DD + oc. 2. 
 
 PLATE 38. 
 
 Fig. 69. Median vertical section of a strobila in the stage of Fig. 26 ; x, boundary between ephyrula and basal polyp. 
 X Zeiss B + oc. 2. 
 
 Fig. 60. Portion of section from the same specimen, showing the proboscis of the basal polyp ; x marks same point as 
 in preceding. X B & L | + Zeiss oc. 2, dt. 160. t 
 
 Fig. 61. Median vertical section of a basal polyp, stage of Fig. 27. X Zeiss B -f- oc. 2. 
 
 Fig. 62. Part of a section from the same specimen, showing the proboscis, p, and the vestige of the former connection 
 with the ephyrula at x. X B & L + Zeiss oc. 2, dt. 160. 
 
 Fig. 63. Median vertical section of an ephyrula that has recently become free ; x is opposite the opening that formerly 
 led into the cavity of the basal polyp. Cf. Fig. 29. x Zeiss DD -f oc. 2. 
 
 Fig. 64. Median vertical section from a young medusa intermediate in age between Figs. 31 and 32. The section is 
 nearly interradial in position, x Zeiss AA + oc. 2, dt. 160. 
 
 Figs. 65 and 66. Tangential sections of the same specimen, parallel to the last, nearly at right angles to an interradius. 
 Fig. 66 is the one nearer the periphery, x Zeiss AA + oc. 2, dt. 160. 
 
 Printed, August, 1900. 
 
MEMOIRS BOST. soc. NAT. HIST. VOL. 5. !" 
 
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 PLATE 33. 
 
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