INTERNAL PARASITES OF THE SEBAGO SALMON From BUI E 1 1 « E < E 3 || 0. E S.S •Eeoe us < ft :« " cr " m £ u 1 1-1 >t . I --d ^ w o"a ' J ; J .f = . ■£§ u< •a : 3 ! 3 £ «;EE u P S i! t ■ ■ of J ^D Ua M X - 5 : I ;i .tg '<; ai ■0 3 c ;s .0 1 IJ !*>. 3 ■>.8 l> 3 . J i a < c SS V , ' «; M B S ' 1 ; c B u ■" '5 -a -a 3 t 1 y ; B ! S 0. "■a • < lISS £< C W 1 ' < 1 bI .| ■o > ! i ' 3 > ^ ; ^ t "t I j 5 ; J S'l c 1 :# 1 It 1 1 I jflll ti S •§' ■o 3 !^ ^ w ;s2 ; •^ >.^ ffi '■^ M i^ X ; >. < .« Pf .{-« . 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S 1 d '' ■a .E 1 S X •z i C c T T h ^ ^ X Je 1 H 1 '■5 3 < > < < < c X ■o J I I s a E 1 a 1 \ £ I ~^ 1 c E i B E i E E C c •c E E e E 3 C 1 S t C J 'I "5 1 5 : I 1 c t 1 c c 1 1 1 ■ail i 1 '^ X S ■! •5. ^ -5 1 s 1 1 I ° c •S E '3 g in < i E £ i I I < c c E E < C E E E E < < 6 c < U. < 1 V I < c i < INTERNAL PARASITES OF THE SEBAGO SALMON. II7I i -•§ i E 2 0." •qx ■at '€ 1 j i Bi See Cestoda. Tetrarhynchus appendiculatus ace. to Rudolphi. E. inflatus ace. to Rudolphi. Host species uncertain. AftprwarHs rpfprrpH to E & i s •i a S X X t c 1 C c c 1 c C C c \ E ■c.S III w j < t > E a •0 W 1 > c 1 0! C T 1 C c i- a 1 i- H > (2 X 1 t (2 a ■c Itfl lllllll! 1 1 |H|||| llf§ IIIIMIIII! Ui f II e c.i IB 5 T ( S i- 1 N t ia c •? 2 :3 S iS J X ^ J •t :: 1 s rt C i: A 1 % X (2 c = i2 1 1 •c £ 1 1 s < ■5 I i < i < c •t s 1 p: c PS 1 I r ti "i J W b: = i J- i : •E c u = E S i 1 W J2 : > 1 i 1 c i 1 c W B i c > n 1 1 1 1 1 c i 1 E ■: BULLETIN OF THE BUREAU OF FISHERIES. PARASITES OF PACIFIC SALMON. The list of parasites for Atlantic salmon in America, though small, is much more extended than the records concerning the Pacific salmon. While tremen- dous numbers of the latter fish, which belong to several species of the genus Onco- rhynchus, are taken every year for commercial purposes, apparently no one has studied the parasitic fauna or done more than to record casually a few data taken during a study of some other factor concerning the species. Kven of such notes I have found only a very few. In a report on the life history of the Alaska salmon, Bean (1890, and also 1893) noted a few items concerning parasites. He mentions the presence in 1889 of numerous intestinal worms in the red salmon and finds that all species of salmon [in fresh water?] are more or less covered with parasitic copepoda. Much more extensive are the notes made by the brilliant young naturalist and student of the Pacific salmon, Cloudsley Rutter, who only a short time back met such an untimely death. In the course of investigations on the natural history of the quinnat salmon in the Sacramento River, Rutter (1902) records some interesting items regarding their parasites. A common pest in the adult of this species in fresh water is a parasitic copepod which attaches itself to the gill filaments. Usually not numerous on a single fish, they yet sometimes destroy the gill filaments almost entirely. The intestine of the spawning salmon is frequently inhabited by tapeworms extending into the coeca and at times filling them completely. They do not occur in the stomach. In 1898 they were much more abundant than in 1900. Among 200 young salmon examined from fresh- water stations in the Sacramento basin in May, 1898, and April, 1899, parasites were found in the stomach contents of 31 fish. They were described as of two or three kinds, one elongated [cestode?], the others short and grain-like [trematodes?]. Rutter thinks that residence in fresh water is conducive to the growth of parasites in the stomachs of young salmon. He gives the following tables of their occurrence according to size of host and dates of capture. Occurrence of Parasites in Quinnat Salmon from S.\cramento River. According to dales of caf>ture. Month. Number examined. Number with parasites. Percentage with parasites. 9 IS Is ■ s 4 3 3 8 3 8 _ May July . - ^ J _ ^ November 20 " X Total- 209 31 ■ INTERNAL PARASITES OF THE SEBAGO SALMON. 1 1 73 Occurrence of Parasites in Quinnat Salmon from Sacramento River — Continued. According to size of fish. Size. Number examined. 1 Number w parasites th Percentage with parasites. 61 57 53 30 8 3 3 1 ^ 38 TotaL 2og 1 31 It will be noted that the percentage of infestation increases rapidly with the size and age of the fish, but this would naturally be associated with the more extensive feeding of the older and larger fish, whether in fresh or salt water. In the absence of comparative data for salt water forms to contrast with these of summer residents in fresh water, it is not allowable to attribute this condition to the delayed migration of these fish, as Rutter does. From brackish-water stations 20 young salmon were examined and parasites found in 3 only. This number is too small to be available for comparison with those fresh-water forms noted above. Unfortunately no further data are available concerning the varieties of parasites found either in the adult or in the young specimens. It is probable that the adult parasites are the same as certain forms to be discussed later from the Alaska salmon. OBSERVATIONS ON THE SEBAGO SALMON. SPECIFIC RELATIONSHIPS The Sebago salmon is regarded by some as merely a landlocked variety of the Atlantic salmon, Salmo salar. found both in European streams and in the rivers of Maine and northward. By others it is viewed as a separate species, Sahno sebago, but in any event closely related to the former. In their extensive catalogue of North American fishes, Jordan and Evermann (1896) include all these forms in the single species Salmo salar Linnaeus, speaking of its range as follows : North Atlantic, ascending all suitable rivers in northern Europe and the regioa north of Cape Cod to Hudson Bay; formerly abundant in the Hudson and occasional in the Delaware, its northern limit in the Churchill, Albany, and Moose rivers, flowing into Hudson Bay; sometimes perfectly landlocked in lakes in Maine and northward, where its habits and coloration (but no tangible specific characters) change somewhat, when it becomes (in America) vars. sebaqo and ouananiche. Similar landlocked varieties occur in Europe. Of the Lake Sebago form which I had the opporttmity of studying and which these authors regard as a subspecies, Sahno salar sebago (Girard), they write as follows : Smaller in size, rather more plump in form, and nonmigratory ; not otherwise evi- dently different. Sebago Pond and northward; introduced into lakes in various parts of the country; seldom entering streams; reaches a weight of 25 pounds. 1 1 74 BULLETIN OF THE BUREAU OF FISHERIES. It is important to notice that the same authors also recognize a second subspecies, and this may be the form from which were obtained the parasites reported by Stafford (1904) and alread}' commented upon. Concerning this subspecies, Jordan and Evermann write that Salmo salar is — * ='= ■■■ represented in Lake St. John, Saguenay River, and neighboring waters of Quebec by the landlocked Salmo salar ouannmrke McCarthy MS., new subspecies. Still smaller, rarely reaching a weight of 7 '2 pounds and averaging 33^. An extremely vigorous and active fish, smaller and more active than ordinary salmon, but so far as known not structurally different. Saguenay River, Canada (outlet of Lake St. John), and neighboring waters. Were it possible to determine definitely whether the records of Stafford concern the oceanic form caught during its migration or the landlocked form, a more definite value could be placed upon his data. In the absence of such information one can not venture to use these records at all in the discussion of the biological problems concerned. What these problems are will be clearer after a more detailed consideration of the case. SOURCE OF PAR.'iSlTES. In view of the close specific connection of the two forms, the European sal- mon just considered and the Sebago salmon, a comparative study of their para- sitic fauna is of unusual interest, especially since the Atlantic salmon spends the greater part of its life in salt water, and after its entrance into fresh- water streams in the course of its migration does not in most cases partake of any food. Consequently whatever parasitic guests it harbors must, as already explained, be of marine origin. The exceptions to this statement are due to accidental infec- tion, and are both small in numbers and insignificant in variety and relative importance. On the other hand, the landlocked Sebago salmon never enters salt water. Its period of active feeding and growth is passed in inland waters, those of Sebago Lake in the case of the specimens we secured and examined. Whatever parasites it harbors are hence obtained in that lake, and are either pure fresh-water organisms or such as have been introduced with the host and subse- quently acclimatized to a fresh-water existence. In the case of such parasitic species as undergo direct development, like many nematodes, the introduction of a marine parasite into fresh water involves the habituation of the free living stage, either egg or larva, or both, to the limnetic environment, and this is the identical process involved in the transfer of any free living organism from a marine exist- ence to one in fresh water. In the case of parasites which manifest indirect development with change of host the case is much more complicated. Such parasites usually have one or more brief stages of free existence in the open water as egg, embryo, or larva, like those just referred to. But they also employ one or more intermediate hosts, in which certain parts of the development are passed. Now, either the same marine animals which serve as intermediate hosts in the sea must be found in fresh water also, or must be successfully INTERNAL PAR.'iSITES OF THE SEBAGO SALMON. II75 introduced at the same time with the primary host and its parasites to which they are related, or, finally, there must be present in the fresh water other animals which can ser\'e successfully as intermediate hosts. The interrelation is thus very complicated and the chance of achieving it so small that in most cases marine forms do not bring the majority of their parasites with them in the transfer to fresh-water existence. In other words, limnetic animals are less heavily para- sitized than marine. For this reason the examination of so recent a migrant into fresh water as the Sebago salmon is of great biological interest. At Lake Sebago only 7 specimens of the Sebago salmon were obtained and examined. These weighed, respectively, 2, 2, 2, 3, 5 J2 , 8, and i6 pounds. While the number examined was from one standpoint small, yet in view of the scarcity of the species in the lake it was fortunately large. The series was also representa- tive of different ages, ranging probably over several years in growth. It seems likely that if marked variations in food materials were found such a range of specimens would indicate the fact through differences in parasitic infestation. Yet there was a striking uniformity in the records in the series. Furthermore, the fish were all examined very soon after capture, and thus any post-mortem wanderings, which certainly do influence the location of parasites collected from market fish, were largely avoided. No doubt there are rare parasites of this species which are not represented in this collection, but, all things being con- sidered, it may be asserted with some confidence that the records give a true picture of the number and location of the parasites infesting them. The parasites found are recorded in the following table : Record of Parasites from Salmo sebago. [x— many. xx=very many. §=niore than in fish no. 14— not counted.) Host. Parasites, number and location. 6 2 In. 16 16 i Lbs. & CEsopbagus and stomach. Pyloric coeca and adjacent part of intestine. Intestine behind py- loric coeca. Body cavity. 14 d 7 Azygia sebago 45 Abothrium cras- I Proteocephalus pusil- lus. I Azygia sebago I Proteocephalus larva. I Bothriocephalidlar\'a. Proteocephalus pusillus. Proteocephalus pusillus _ I Bothriocephalid larva- I Nematode A. 15 13 Azygia sebago § Abothrium cras- 16 27 8 d XX Azygia sebago a 70 Abothrium cras- I large Bothriocephalid larva. I small larval cestode 17 33 16 6 d I Azygia sebago 18 Azygia sebago 30+Abothrium eras- sum. 80 Abothrium cras- 33 Nematode B.& 19 2K 5'A d d XX Azygia sebago 19 Azygia sebago X Abothrium cras- 50 Abothrium eras- encysted in spleen. 3 Nematode A. ling bladder (?). See text. 6 Viscera a mass of adhesions; parasites difficult to pick out. 1176 BULLETIN OF THE BUREAU OF FISHERIES. A NEW TREMATODE PARASITE. Every one of the 7 fish examined contained specimens of a new trematode, which I have named Azygia sebago. It is relativefy insignificant in size and difficult to detect amid the thick white nmcus which fines the wall of stomach and ojsophagus. Not a single host was without this parasite, and several salmon sheltered considerable numbers ; yet in most cases they were not seen in life, but only appeared after the stomach and its contents had been agitated in a pre- serving fluid. Careful examination of the debris then never failed to disclose some specimens of this worm. Moreover, it was the only species of trematode that was found in the vSebago salmon. The description of the species may properly precede a discussion of its biological characteristics. The genus Azygia was established by Looss (1899, p. 569) to include a well- known European species, Disiomum tereticolle Rudolphi, which was made the type of the new genus. It was also the only species in the genus ; for, as Looss remarks, he had not been successful in finding among the flukes that he knew any form which could be included naturally with the old species, Distomum tereticolle. There are at the disposal of the student several good descriptions and delinea- tions of the old species, Azygia tereticoUis Rudolphi, so that it is possible to determine with precision its structural features ; the best of these descriptions is undoubtedly that by Looss (1894). The new species, Azygia sebago, "■ is much smaller than the older form, measuring 10 mm. in maximum length and averaging 5 to 6, or less often 8 mm., in well-developed specimens. Fortunately, I have a large range of sizes, from such as are only barely, over i mm. in length to the maximum noted, so that it was possible to follow the changes accompanying the assumption of the adult form. Specimens 2.85 mm. long have not yet produced ova. The general form of the body is cylindrical, bluntly rounded at the anterior end, and tapering slightly toward the posterior end, which, however, is ulti- mately rounded oft'. The body is regularly divided into two regions by a shal- low furrow at which the direction of the long axis changes more or less (fig. i), giving the worm in lateral aspect much the appearance of a can-top tightener. While the relation of the regions is very variable, at times forming almost a sin- gle straight line and again standing at a considerable angle with each other, yet one can make out these conditions even in specimens which are poorly killed and badly distorted. The anterior region assumes the form of an ellipse surrounding the two suckers. This region changes relatively little in size with growth. In one of the smallest specimens measured (1.6 mm.) the distance between the "During the spring of 1908 two of my students, Messrs. W. N. Anderson and H. B. Boyden, made a study of this form and prepared a partial report on its structure, to which I am indebted for some of the data in the following description, and also for two figures. INTERNAL PARASITES OF THE SEBAGO SALMON. 1 1 77 centers of the two suckers was 0.5 mm. In one 10 mm. long this distance measured i mm. The posterior region is nearly a perfect cylinder until shortly before the tip, where it tapers somewhat. In some specimens the posterior end is consid- erably inflated and appears semitranslucent. This is undoubtedly due to the distended condition of the excretory reservoir, which inhibits contraction of the circular muscles in the portion of the skin adjacent to it. The breadth of the body varies according to the degree of contraction, but may be estimated in general as from 0.7 to i mm. An immature specimen 2.85 mm. long measured 0.65 mm. in breadth between the suckers, 0.6 mm. behind the acetabulum, and 0.52 mm. behind the posterior testis. An imma- ture specimen only 1.6 mm. in length measured 0.32, 0.28, and 0.21 mm. in breadth at the same points. In cross section the body is round or very slightly oval. The oral sucker is subterminal and its opening looks almost directly ventrad. It is rather conspicuous, and in an average specimen measured 0.68 mm. in antero-posterior diameter and 0.67 mm. transversely. The depth in the same specimen was 0.6 mm. The orifice is nearly circular, though often appearing slightly flattened along the posterior margin. In an immature specimen 2.85 mm. long the oral sucker measured 0.35 mm. in antero-posterior diameter and 0.4 mm. laterally ; the orifice measured 80 by i so /i. The ventral sucker or acetabulum is usually distinctl}' smaller than the oral. In the extreme case it appears about equal in size or, on the other hand, only about half as large. Ordinarily it is prominent, but in short, thick specimens it is almost hidden, whereas in elongated, slender specimens it projects so far as to appear almost pedunculate. It is also often slightly oval in a transverse plane. In an adult specimen it measured 0.57 mm. in antero-posterior diameter and 0.69 mm. laterally. In a specimen 2.65 mm. long the corresponding meas- urements were 0.3 and 0.33 mm., and the orifice measured 52 by 80 /i. The alimentary canal opens in the oral sucker, close behind which lies the pharynx without any prepharj'nx between the two. The pharynx measures 0.21 by 0.13 mm. It is often seen in the vertical position represented in the figure of Messrs. Anderson and Boyden, which I have taken the liberty of copying here. The oesophagus is very short and it often proceeds anteriad from the upright pharynx, as shown in the drawing (fig. 3, pi. cxxi). At its tip start the two branches of the intestine, which also usually extend forward a short distance and then turning posteriad continue almost to the extreme posterior tip of the body. These crura being longer than the body in the usual specimen are thrown into folds, which often appear as if the canal possessed irregular outpocketings, such as one finds in Paragonimus. Observations both on the living material and 1 1 78 BULLETIN OF THE BUREAU OF FISHERIES. on serial sections show positively that such is not the case, but that the crura are simple tubes. The number of folds, twists, and turns depends upon the degree of contraction and usually appears greatest between the acetabulum and the ovary. The excretory system is very characteristic of the genus Azygia. An elongate carrot-shaped collecting reservoir or bladder extends from the excretory pore, which is located at the posterior tip, through the center of the body anteriad to the posterior testis. The wall is heavy and is thrown into folds which appear at intervals projecting slightly into the cavity. From the anterior end of this reservoir two tubes pass off, right and left, which are at the start dorsal to the posterior testis; they soon pass toward the ventral surface, but cross the acetabulum on its dorsal aspect and dorsal to the oral sucker and are reflected posteriad. During their entire course they lie within the intestinal crura and usually ventrad to it. Their heavier walls indicate clearly that these conspicuous tubes are more nearly analogous to the collecting reser- voirs of other flukes than to the delicate excretory vessels which here also are seen connecting with the tubes and the reservoir at various points. The three germ glands, the ovary and two testes, lie close together in a longi- tudinal row distant from the anterior end about two-thirds the length of the worm. The ovary is most anterior and smallest of the group. An unusual morphological feature is the inclusion of the shell gland, a small yolk reservoir, the ends of the yolk ducts, and the first coils of the uterus within the same capsule that incloses the gland proper (fig. 6, pi. cxxi). The relation of the ducts as worked out by reconstruction is represented in figure 5 after the studies of Messrs. Anderson and Boyden. This resembles closely conditions as shown by Looss (1894) foi" ^- it^f'cticollis, although I do not find that he has noted the massing of organs within a common capsule. The uterus extends forward in numerous short coils which all lie within the intestinal crura until at the acetabulum it merges into a short, heavy-walled metraterm. The latter passes dorsal to the acetabu- lum and ventral to the cirrus pouch into the genital cloaca, with an inconspicu- ous genital pore located just anteriad to the acetabulum. The vitelline glands lie along either side of the worm exterior to the intestinal crura. They begin a little behind the level of the acetabulum and extend to a point about halfway from the posterior testis to the end of the body. This constitutes perhaps the most striking morphological difference between this species and Azygia tereticol/is, in which the vitellaria do not pass posteriad of the posterior testis. This conspicuous difference in the extent of the vitellaria enables the student to differentiate the two forms at a glance. Attention should be called to the fact that on account of this structural feature a correction must be made in the generic description of Azygia, in which IXTERNAL PARASITES OF THE SEBAGO SALMON. 1 1 79 stress was originally laid on the extent of the vitellaria. The condition of the vitellaria in the older species has also been employed by Pratt (1902) as a char- acteristic of the genus in elaborating his key for the determination of the flukes. Although typically a member of the genus Azygia, the present form would fall in another genus according to the terms of that synopsis. No one who sees a specimen or reviews the structure of this form can doubt its relationship; the precise extent of the vitellaria is evidently a subordinate feature, and as such of specific rank only. The follicles of the vitellaria are distinct, regularly oval bodies, lying in two longitudinal rows on each side with a more or less conspicuous break oppo- site the ovarv between the anterior and posterior series. The follicles measure from 0.06 to 0.07 by 0.03 to 0.04 mm. The symmetry of the rows is in places interrupted by extra follicles, making at such points three rows of follicles instead of two as usual. The ducts from the anterior and posterior series unite opposite the ovary to form a common transverse duct which at the center of the body joins its fellow from the opposite side. At the point of union there is a small yolk reservoir. As already noted, this is included within the common capsule which surrounds the ovary and is ordinarily not visible except in sec- tions. Laurer's canal is present and opens on the dorsal surface just posterior to the ovary. It does not have the enlargement ordinarily called a seminal receptacle, but is usually somewhat coiled and lies on the left side of the ovary. This may be an adaptation to the extreme variations in length so character- istic of this worm. The eggs are small; an average of 50 measurements places their size at 48 by 27 iJL, which is slightly larger and broader than those of .4. tereticollis, accord- ing to the measurements given by Looss (1894). The testes are oval bodies lying one directly behind the other and that behind the ovary. The three organs are separated only very slightly from each other. The outline of the testes is smooth and measures 0.42 to 0.46 by 0.59 to 0.6 mm. with the major axis transverse. One can usually distinguish that the two are not equal in size. The coiled seminal vesicle and a poorly devel- oped cirrus with prostate lie in a common connective tissue capsule, the cirrus pouch, which stands immediately anterior to the acetabulum. The pouch measures about 0.23 by 0.17 mm. in diameter. It opens anterior to the metra- term into the genital sinus already mentioned. One histological feature deserves consideration here because of its con- spicuous character. In sections of Azygia sebago one notices certain muscle elements which are so prominent and regular as to deserve almost the name of a layer; they occur within the parenchyma, far removed from the usually rec- ognized dermal layers and at a point where ordinarily one finds only scattered Il8o BULLETIN OF THE BUREAU OF FISHERIES. dorso - ventral or oblique fibers which are not subject to any regularity in arrangement. These are longitudinal fibers extending from the oral sucker throughout the entire length of the distome, as is clearly seen in a frontal section (fig. 4, pi. cxxi). In position they lie one-fourth to one-fifth the radius of the section distant from the external surface. The cross sections of these fibers show them to be much heavier than the other muscle elements and to occupy an oval zone parallel to the outer surface of the body. They divide the body accordingly into a cortical and a medullary portion. The vitellaria are the only conspicuous organs which lie in the cortical layer. This muscle layer is undoubtedly related to the marked contractions of the fluke which have already been commented upon. Unfortunately I have no material available from which to determine whether similar fibers also exist in .4. tereticoUis. Looss (1904) does not mention them. The relations of oral sucker, pharynx, and crura, the convolutions of the intestinal branches, the coils of Laurer's canal and of various ducts and the sinuous course of the collecting tubes in the excretory system all point toward the variable extensibility of the worm. Differences in caliber and in the dis- tance between organs also indicate the same. Observations on the living parasite serve to show that it is constantly extending and contracting the body to such an extent as to double or halve the length within a few seconds of time. In fact, I have never before observed a form which indulged in such energetic twisting and contracting. This habit renders any observations on the living worm very difficult. Looss (1894, P- 7) comments on the active migration of .4. tereticoUis after the death of the host, a feature previously recorded for D. cylindraceum by Braun (1890, p. 568). .4. sebago manifests the same tendency in the most marked degree. The normal seat of this parasite I feel sure is the stomach, and perhaps the oesophagus also, but even a slight delay in the examination of the host resulted in finding single specimens well down the intestine as well as up in the pharynx and even among the gill filaments. In one case a salmon caught late in the day was kept overnight to be photographed, as it was a peculiarly fine specimen. When the viscera were examined, about twenty hours after the capture of the fish, my field notes record that there were 36 dis- tomes in the air bladder and that they were seen coming in through the ostium with mucus from the oesophagus. Other specimens were found in the pharynx and gill cavity and one even in the body cavity. The last can be attributed no doubt to some tear in the alimentary lining which permitted the fluke to make its way unhindered into what is ordinarily a closed cavity. In still another salmon which had gorged itself on smelts my field notes contain com- INTERNAL PARASITES OF THE SEBAGO SALMON. I181 ments on the activity manifested by these distomes, which cHmbed about on the smelts and in them as they lay half digested in the stomach of the salmon. This was so noticeable that I turned my attention at once to the smelt " to ascertain if perchance it played any part in the life history of the distome. In all, I have records of 52 smelts examined, and in 46 of these were found speci- mens of Azygia sebago. The parasite occurred in the stomach only and the infestation was small, from i to 14 distomes being found in each host, with an average of only 4 to a fish. In most cases the parasites which were taken from the stomach of the smelt were immature, not having yet reached that size at which the production of ova begins; they were on the average 3 to 4 mm. long, or in some cases even smaller, running from 1.5 to 2.5 mm. in length. Single specimens reached a length of 6, 7, and even 10 mm. In one case, indeed, there were none shorter than 6 mm., and the specimens varied from that to 10 mm., so that one can not fairly maintain that they never reach the size attained in the salmon. Nevertheless, after the account is cast up the average shows dis- tinctly that the distomes do not reach their full size in the smelt and, so far as collections made during July and August can indicate, those taken from this host are usually small in size and sexually immature. I did not obtain any information as to the source from which the smelt acquires its infection, but in view of the universality with which smelt form the food of the salmon in Sebago Lake the latter undoubtedly owe to them the major portion of their infestation with this parasite. The host record of Azygia sebago is even yet unfinished. In the course of my work numerous other fish from these same waters were examined. In young specimens of Esox reticulatus 6 to 16 inches long I found this same para- site reasonably abundant. To be sure, they seemed to average somewhat longer, being 10 to 12 mm. in length in material from one host and 10 to 14 or even 18 oThis fish I am compelled to designate under the name Osmerus mordax (Mitchill), as Jordan and Evermann (1896) do not recognize the Sebago smelt as a separate form, saying of the species "Atlantic coast of the United States from Virginia northward to Gulf of St. Lawrence, entering streams and often landlocked." I am inclined to think that even in Sebago Lake there are two smelts. My atten- tion was first directed to this possibility by Dr. W. C. Kendall, who, recalling our previous discussion, writes as follows in a recent letter: "You may recall that there seem to be two forms in the lake differing somewhat in size and habits. The large form, which is the one that we caught with hook and line, is nearer to the marine smelt. The small form is the one that we found in the salmons' stomachs. You will doubtless recall that the principal food, when any at all was found in their stomachs, of the large form was small fish, generally young smelts. Our examinations of the stomach contents of the small form show Entomostraca almost exclusively. This difference is indicated also by the gillrakers, which are more numerous in the small form." These distomes occurred equally in both sorts of smelt and those from the smaller smelts were larger than those from the larger fish. This is, of course, a mere accident, but it serves to show that the two types of smelt conduct themselves alike toward the parasite. Il82 BULLETIN OF THE BUREAU OF FISHERIES. mm. long in that from another host. In the latter it was noticeable that the suckers protruded very conspicuously and the body was much smaller in caliber than in the specimens from the salmon and the smelt. Yet in the absence of any structural differences I am forced to conclude that this contrast in size and general external appearance is due to some slight difference in the technique employed or in the condition of the parasites when they were preser\'ed. This is all the more probable when one considers that in one case the specimens from Esox were identical in appearance with those from the salmon. This parasite was found in all but one of the dozen specimens of Esox reiiculaius examined, being present in the stomach in numbers of i to 80 in each host. In two cases a single specimen was found in the intestine, perhaps due to some post-mortem wandering on the part of the parasites. In 4 specimens oi Anguilla cluysypa out of 9 examined I also found Azygia sebago in the stomach, but in small num- bers only, averaging 3 to each host. Finally 2 of these distomes were found in a single Pcrca flavescens, here also in the stomach. In order to give a ready comparison, I append hereto a table of similar measurements from a series of this distome taken from the various hosts men- tioned. The difference in length indicates in part age and in part method of preservation. In fact, it is difficult to achieve any uniformity among speci- mens so exceedingly active as this species. Measurements of Azygia sebago. Serial No. Host. Length. Ante- tip to cen- ter of oral sucker. Diam- eter of oral sucker. Dis- tance be- tween ters of suck- Diam- eter of ace- tabu- lum. Ante- tip to ter of ovary. Dis- tance be- tween ter"of ovary and ante- testis. Dis- tance be- tween ters of testes. Dis- tance from poste- testis to pos- terior tip. Breadth between suckers. Breadth behind acetab- ulum. Breadth behind poste- testis. 16 74-79 60 96 7-8 46 From Salmo _ . . From Osmerus. do do." From Esox From Perca M,n. 8.7S 2.8s 1.64 4.08 Aim. """38" . 29 Mm. 0. 74 ■ 4 .25 .56 ■ 72 • 51 by. 57 Mm. 1.38 .62 ■4 "l"84' .78 Mm. 0.6s .33 ■ 37 • 55 .35 by . 4 Mm. 4.76 1.6 .89 Mm. 0.31 Mm. 0. 62 Mm. 307 ■ 55 Mm. I. 29 .6s :Vs ■ 75 • 71 Mm. Mm. 1. 38 1.23 :^8 -.W 7.88 2.69 .9 ■ IS ■ 91 • 19 3.25 I. 16 ■ 77 . 77 • -4 •5S a Much elongated: poor technique: preserved by helpe: The question naturally presents itself, Has this form been seen by others previous to the present date? The records on the subject are scanty, but they throw some light on the question. INTERNAL PARASITES OF THE SEBAGO SALMON. I183 Leidy has described (1851, p. 206) a form as Disioinum ierreticolle '^ Rudolphi, which Pratt (1902, p. 957) lists as Azygia tereticollis (R.) Leidy. The original description is as follows (Leidy, 1851, p. 206) : Distomum terreticolle, Rud. Entoz. Syn., p. 102; Dujardin, Hist. Nat. des Helm.; Diesing, Syst. Helm., p. 358. Body subcylindric, light flesh color, posteriorly rounded. \'entral acetabulum (^ line) 1.6 mm. behind the oral (!^ line) 0.7 mm. in diameter. Oral acetabulum ('^ line) 0.5 mm. Length (8 lines) 16.8 mm.; breadth posteriorly {% line) i mm., anteriorly ('^ line) 0.7 mm. Habitation. — Stomach of Esox rcticulaius Lesueur. Remark. — The generative aperture is placed immediately in advance of the ventral acetabulum. When the animal contracts, the two acetabula are nearly brought into contact. The description is scanty, and yet one can say with some assurance that the form before Leidy was not the European species named by Rudolphi and dis- cussed by a long series of authors, of whom Looss (1894) has given the most complete description with truly admirable figures. Leidy's specimen is much too small for average adults of Azygia tereticollis, which is, moreover, cylindrical instead of broader posteriorly, as was Leidy's worm. Again, Azygia tereticollis has the oral sucker larger than the acetabulum, whereas in Leidy's form the reverse is true. Finally the suckers in Leidy's form do not agree at all in size with the suckers in Azygia tereticollis, as described by Dujardin and others. It is somewhat more diffictilt to say whether the form before Leidy was the same as that I collected in the Sebago salmon. In size the two are not very different, although Leidy's was larger. Other measurements do not agree at all well. The sizes given for the suckers are just about reversed. The final determination of this point, however, must await a reexamination of Leidy's original material. The only other reference to the occurrence of Azygia on this continent, so far as I know, is the brief note of Stafford (1904, p. 488) , in which he records Azygia ^ tereticollis Rudolphi from mouth, pharynx, oesophagus, and stomach of Esox lucius Linnaeus, Lota maculosa Le Sueur, and Ameiurus nigricans Le Sueur. Absolutely the onlv data concerning the worm which Stafford records is the size, 12 by I mm. Now, this does not agree with adults of -4. tereticollis, for Looss (1894, p. 18) says of that species that the first eggs are not set free into the uterus until the worm is 8 to 10 mm. or more in length, and these are uniformly abnormal and defective. In another place he remarks (1894, p. 7) that in most cases eggs are found in worms 12 mm. long, although in scanty numbers. I am of the opinion that Stafford did not have before him the true .4. tereticollis a The text by error contains terreticolle for the specific name instead of tereticolle. 6 Unfortunately, Stafford spells the genus Azigia and the species tereticolle. Il84 BULLETIX OF THE BUREAU OF FISHERIES. and incline to the belief that the form which he observed may have been the species under discussion. The European species, . I £:ji'(7/a tereticol lis, has been reported homEsoxlucius, Lucioperca sandra, Lota vulgaris, Truita variabilis, Saimo trutta, Salmo fario, Salmo hucho, Salmo alpinus, and Salmo salar. All of these save Salmo salar are fresh-water fish, and the parasite may be regarded as a characteristic of fresh- water species. The American species, Azygia sebago, I found in Salmo sebago, Esox reticulatus, Osmerus mordax, Anguilla chrysypa, and Perca flavescens. Stafford recorded what may have been the same from Esox lucius. Lota maculosa, and Ameiurus nigricans. These include strictly fresh-water forms, landlocked species, and one migratory fish, but inasmuch as the records have been taken in fresh water even the last host does not constitute any evidence against the fresh- water habitat of Azygia sebago. Its congener, Azygia tereticollis , found by Mcintosh in the salmon of the Tay, formed part of the evidence that this host feeds during its fresh-water residence. Equally here we may regard A. sebago as a fresh-water element acquired by its host since the latter became landlocked in Lake Sebago. The presence of the parasite in several other characteristic fish of the same water basin is clear evidence of the sources from which it might have come. CESTODES. Cestodes constituted the most conspicuous element of the parasitic fauna. Every salmon opened contained a mass of large worms in the pyloric region. They lay with the head and anterior portion of the body in a pyloric coecum usually at or near its tip. The worms were large and the body was thrown into loops which occupied the initial coecum and folded through the intestinal canal into other ca'ca, often crowding them full apparently to bursting. Viewed from the body cavity, even before the viscera were opened, one could distinguish the coeca which contained the parasites by their opaque, chalky appearance in distinct contrast with the translucent character of those coeca in which there were no tapeworms. When the intestine was opened it appeared full of the cestodes, which protruded in loops hanging from the coeca into the cavity or crossing into other coeca in a tangled mass, in several cases large enough to distend the wall conspicuously. The anterior coeca were those primarily or chiefly occupied by the worms and although often the entire cavity of the intestinal canal was crowded full of parasites, it was noteworthy that they rarely if ever entered any of the posterior coeca. When few worms were found they lay with the scolices at least in the coeca of the most anterior region. The species to which I have referred in the preceding paragraph is the well- known Bothriocephalus infundibuliformis, according to Liihe (1899) more cor- rectly designated Abothrium crassum, which is so common in the Atlantic salmon INTERNAL PARASITES OF THE SEBAGO SALMON. II 85 from various parts of Europe. Of its occurrence in the Rhine salmon, where it is found in 42 per cent of the specimens examined, in 91 per cent of the Baltic salmon, in 26 per cent of the Tweed salmon, in most of the Tay salmon and of the Irish salmon, enough has been said in the historical survey. It is a typical salmonid parasite, and is found even in eight species of that family which inhabit fresh water. Its presence in the landlocked Salmo scbago, which confines its life cycle to fresh water, is hence not surprising. Evidently the life cycle of the species permits of easy adaptation to a fresh-water existence, for I have to report its occurrence not only in the host under discussion, but also in another promi- nent American salmonid, the Great Lakes trout, Cristivomcr namaycush (Wal- baum). It was found abundantly in specimens of this host which I examined in July and August, 1894, at Charlevoix, Mich. From 30 to 80 tapeworms of this species were present in each Sebago salmon, and neither size nor age played any evident part in determining the degree of infestation. Absolutely every one of the salmon taken was infested. In considering the possible life history, I naturally turned to the Sebago smelt as the host of the larval form, probably a plerocercoid, and examined a number of these fish with great care, but was unable to detect the lar^^a, if indeed it was present. Nothing was discovered which throws any light on the life cycle. It is worthy of note that all of these parasites were full grown; not a single specimen was found which was not dis- charging ripe proglottids. Consequently the infestation must have taken place somewhat earlier in the year. It would take observations at other months to determine when; and the food at that time would evidently be the source of the parasite. In addition to this dominant species some other cestodes were also recorded. A few fragments of a small species of Proteocephalus were found in each of four hosts, and a larval form, which probably belongs to the same Proteocephalus, was obtained in each of two hosts. Two different bothriocephalid larvae of small size also occurred each in a single salmon. The four forms just mentioned were all found in the intestine. The insignificant size of a new species of Proteocephalus found and the small number of individuals present in any one host resulted in its being overlooked at first, and it may easily have been present in more hosts than shown by the records. It was found in four out of the seven salmon examined, but in one case only a few loose proglottids were discovered by accident among material from the intestine. A careful examination in comparison with the descriptions of known species leads me to the view that this is a new species to which the name Proteocephalus pusillus may be given. The salient points in the descrip- tion of this new species are as follows: Proteocephalus pusillus nov. spec. — Adult cestode with short strobila, meas- uring only 30 to 50 mm. in length. Proglottids scanty, segmentation 1 1 86 BULLETIN OF THE BUREAU OF FISHERIES, distinct. Head much contracted. Neck i to 1.5 mm. long by 0.21 mm. broad. First proglottids 0.09 mm. broad, changing gradually until in mature proglottids the length greatly exceeds the breadth. Ripe proglottids measure 0.84 to 1.4 mm. long by 0.18 to 0.35 mm. broad. Terminal proglottids present and fertile. Sexual organs typical for Proteoceplialiis; uterus median, with 10 to 14 lateral outpocketings on either side. Testes numerous, within vitellaria. Genital pore lateral, one-third to two-fifths of length of proglottid from anterior margin of same. Ovaries bilobed, median isthmus indistinct, anteroposterior diameter nearly equal to breadth of both lobes. Only a few specimens obtained from a single host species, Salmo sebago. This species approaches most nearly to P. ocellata and P. percce among known species. Unlike the new species, however, both of these older forms have a fifth sucker, fewer lateral uterine outpocketings, a longer neck, differently shaped ovaries, and markedly different proglottids. In specimens wnth developed proglottids the head was so much contracted or distorted that any special description would be of little value. One could easily observe the general features characteristic of the genus. There was no well developed terminal or fifth sucker, and the end organ, which is known to replace it in many forms of this genus, was inconspicuously developed, if present. Personally, I incline to the view that on more careful examination this structure will be found in all species, even those in which its absence has been made a matter of record. Accordingly, not much weight can be put in its presence or absence in any individual case." Three plerocercoid larvae or young cestodes were found in company with Proteocephalus pusillus, which I regard as young forms of this species. The largest came from the salmon which was most heavily infected with this cestode parasite. It was 3.15 mm. long and had begun to assume clearly the appear- ance of an immature cestode. The head measured 0.3 mm. wide by 0.26 mm. long, and the suckers 0.14 mm. in length by o.ii mm. in width. The neck was slightly narrower than the head, but was not clearly set off from the body, which was very uniform in diameter and measured 0.25 mm. in average width. The posterior end of the body was swollen into a rounded knob about 0.35 mm. broad and of approximately the same length. This feature was evidently produced by a powerful contraction of the terminal region of the body. In and near it one could see very indistinct indications of proglottid formation. In form, size, and general aspect this young cestode was in full agreement with the anterior regions of the mature cestodes of this species with which it was oFor a more definite discussion of this peculiar structure so variable in development in the cestodes of this genus, I would refer to a paper now in press by my student, Mr. George R. La Rue, to whom I am indebted for a comparison of this material from Salmo sebago with preparations of other species of Proteocephalus INTERNAL PARASITES OF THE SEBAGO SALMON. II 87 associated. The head, which was not contracted, showed on careful study the deUcate outhne of a rudimentary end organ. While such a structure was not demonstrated in the mature individuals described above, one can say positively that if present it could not have been seen owing to the greatly contracted condition of the adult scolices. I believe that its presence will be demonstrated in more favorable specimens. The complete agreement of this largest larva with the mature specimens in all other features compels me to regard both as different stages in the development of the same species. The other larvae were still in early stages of development, and probably had been ingested by the salmon at a very recent date. Their relationship is not so clear in all respects, and yet I do not hesitate to associate with the new species of Protcocephalus a plerocercoid or young cestode obtained from the same host as the adult worms and the older larva just described. The head is broadly conical, without furrows, and measures 0.3 mm. in breadth. The suckers measure 60 to 75/x in diameter. There is no rostellum or fifth sucker to be found, while the end organ is so poorly developed as to be visible with difficulty and only under the most favorable circumstances. The neck is nearly as broad as the head. In general appearance this larva resembles the adult cestode and the older larv^a previously described. With some reserve one may also assign to this species a single plerocercus taken from another specimen of Sahno sebago. The head, which measures only 1501J, in breadth, is shaped like that of the young cestode and like it is without rostellum or fifth sucker, while the end organ is difficult to demonstrate. Neither furrows nor ridges are seen on the larva, which has a total length of 1.14 mm. The sucker measures only 30 to 45/i in diameter. The neck is slightly narrower than the head. This form certainly belongs to the genus Protcocephalus and probablv to the species already described. From the scantiness of the material obtained one might infer that the Sebago salmon is only a casual host of the species. Yet I did not secure this parasite from any other fish in Lake Sebago and adjacent waters, and I have not met it in fish examined in other places. The presence of larvae in different stages of development with only a few adult specimens in any one host, although some were found in the majority of the salmon examined, would rather favor the view that the cestode was a regular though infrequent parasite of this host. Sparganum sebago, nov. spec. — In addition to the cestodes already men- tioned, there are to be noted two specimens of bothriocephalid larvae which deserve more extended mention. The first was taken from the spleen of one salmon. It measured 25 mm. in length and 1.8 mm. in maximum diameter. There is no neck, but the bodv 1 1 88 BULLETIN OF THE BUREAU OF FISHERIES. increases slightly in breadth for about one-quarter of the entire length and then tapers gradually to the posterior end, which is rounded off. The body is elliptical in cross section without any segmentation, but with numerous rather prominent annular wrinkles. It seemed as if the margins of the body were thicker than the center. The head was retracted. (Fig. 7 and 8, pi. cxxi.) The second specimen (fig. 9 and 10, pi. cxxi) was found free in the body cavity of another salmon. It was 36 mm. long and 0.86 mm. in breadth. The body was somewhat thicker than in the other specimen, but less deeply wrinkled, and the center was certainly thicker than the margins. In this, as in the color and texture, it appeared different from the first specimen. There was no neck. The head measured 0.31 mm. in transverse diameter and 0.43 mm. from the apex to the base of the grooves, which were keyhole shaped. The groove measured 0.25 mm. in transverse diameter at the anterior end and 0.09 near its posterior end. In spite of the differences in appearance noted above it is easily possible that the two specimens belong to the same species and I have preferred to list them for the present under a single heading, naming the form Sparganum scbago. A word should be said with regard to other hosts for these cestodes. Abothrium crassum was not found in any other fish examined at Sebago Lake. Larvae of Proteocephalus and of some bothriocephalid were found in a very few cases in other fish taken from these waters. There were none, however, of which it could be said with reasonable certainty that they were the same as the forms collected from the vSebago salmon and mentioned above. The question of the occurrence of such salmon parasites in other hosts of this region must be left entirely open for the present at least. NEMATODES. Nematodes were not common. They occurred only in half of the specimens of salmon examined and were not abundant. In one salmon t,^ of these worms were obtained, but in the other three only a dozen all told. Accordingly they seem to play only a minor part in the parasitic fauna of the Sebago salmon. They belong to two or three separate species, which are radically distinct. Thus far I have not been able to make a satisfactory determination for any of them, owing to the scantiness of the material and to its unsatisfactory condition. This much can be said: They do not belong to any of the species, or even to the genera, heretofore recorded for the Atlantic salmon. A few notes may be added here concerning these forms. A small nematode was found in the stomach and in the body cavity of two salmon. In all there were only six individuals of this species. I have not been able to satisfy myself that the individuals recorded as from the stomach really belong there, but incline to think that they were adherent to the external INTERNAL PARASITES OF THE SEBAGO SALMON. I189 surface of the stomach and passed unnoticed when that organ was opened and shaken in a preserving fluid in order to collect the small specimens of Azygia sebago concealed in the gastric mucus. Subsequently they were found in the material obtained in this process. They are probably true parasites of the body cavity. Since an approximate determination may easily be misleading I forego all attempt to name this form and designate it for the present simply as "Nematode A." The group of t,t, nematodes obtained from the body cavity was a source of great surprise. These worms are identical with a form found in very large num- bers in the Alaska salmon. Since, however, this species is to be discussed at length in the section of my report which deals with that host, it seems wise to omit here any details and refer to the worm simply as "Nematode B." It is a large form belonging to the Filariadae, but so delicate that it is almost impossible to obtain perfect specimens, and it has thus far proved beyond my skill to preserve any in a complete condition. It has been an exceedingly interesting object of study and will receive at an early date, in connection with the records of the Alaska salmon and its parasites, that detailed consideration which its frequence and its interest warrant. The six nematodes recorded from the stomach were collected and preserv^ed by an assistant. They are in very poor condition, so that any determination can hardly be more than an impression, but the only real reason why I hesitate to refer them to the same species is that in all the thousands of specimens from nearly 200 hosts which I handled in the course of my investigations on the Alaska salmon I never once found the species any- where save in the body cavity. It is not impossible that these specimens were reported from the stomach through some error. As repeated examination is bringing me more and more firmly to accept the identity of this lot with those which I collected personally from the body cavity of the Sebago salmon and of the Alaska salmon, I am being forced to assume the existence of some error in recording them as from the stomach. In any event, it may be said that not more than three species of nematodes are present in the Sebago salmon and that these species are only infrequently and scantily represented in this host. None of the nematodes were found in any other fish examined at Sebago Lake, nor are they known to me from fish of any fresh-water locality in this country. Thus far also I have failed to find any reference in the literature which could be construed as indicating either of these forms. RESUME AND CONCLUSIONS. The first general conclusion to be drawn from this study of the parasitic fauna of the Sebago salmon is that the total number of parasites recorded from this host is small. In all, there have been listed only i trematode, 2 cestodes, 4 (?) cestode larvae, and 2 nematodes, or a total at most of 9 species 1 1 go BULI^ETIN OF THE BUREAU OF FISHERIES. of parasites. To be sure, the number of hosts examined was small, and this mav account for the low total record. Two of these parasites, Azygia sebago and Abothriiim crassum, were found in every fish examined, and each of six other parasites was found in two hosts. This may be compared with Zschokke (1S96, p. 824), who records the parasitic census of losalmon from the North Sea. In these 10 fish were found 10 species of parasites. A trematode and a cestode occurred each in 9 of the fish examined. The cestode was Abothrium crassum, the same species as that found in every Sebago salmon; the trematode was Distomum ocreaiuni, a purely marine form, and hence in sharp contrast with the abundant trematode in the Sebago salmon, which is a member of a characteristic fresh-water genus. This contrast, as well as several other details commented on in the previous pages, seem to indicate the fresh-water aspect of the parasitic fauna in the Sebago salmon. The conditions in the Sebago salmon are all the more striking when one considers the forms which are not found among its parasites. Reverting first to the trematodes, one notices that the only genus represented luere, Azygia, has been recorded from the Atlantic salmon in Europe only in a single case, while here its representatives were found in every host examined. On the other hand, Derogenes varicus, recorded from a good percentage of European salmon in all localities, was not seen even once. The other distomes recorded by European observers in various regions, and often as fairly frequent parasites of the salmon, are entirely wanting in Sebago salmon. Azygia is the only purely fresh- water distome found in European salmon; it is the only distome found in the Sebago salmon. The other distomes recorded in European salmon are purely marine species, or very largely so, but none of them occur in the Sebago salmon. Among the cestodes conditions are identical. The common form, Abothrium crassum, is confined to salmonids, without reference to their habitat, and is as common in fresh-water species as in marine. On the other hand, those cestodes which are typically marine, like Rhynchobotlirium paleaceum, Scolex polymorphus, and the several species of Tctrarhynchus, are absolutely wanting in the vSebago salmon. The various cestode lars^ae are too little known to justify their con- sideration in this connection. They are not referable, even indefinitely, to either habitat. To this statement one must make two exceptions. Scolex polymorphus, recorded from the salmon in Europe, is typically marine, occurring in many sea fish, even though several species may be indicated under the single name. On the other hand, the larva of Proieocephalus is equally typically limnetic and it is recorded from the Sebago salmon only unless the single record of Tania sp. for a larva from the salmon in the Tweed should be referred to this form. In this group again it appears clear that the marine parasites of the European salmon are wanting in the Sebago species, that the only cestodes INTERNAL PARASITES OF THE SEBAGO SALMON. II9I identical in the two forms are such as are clearly fresh-water species, and that the Sebago salmon contain at least one clearly fresh-water genus which is not reported from the corresponding European host. Among the nematodes the evidence is less conclusive, since the amount of material is smaller; .indeed, hardly enough to form a basis for any conclusions. At the same time, all the species which give to the parasitic fauna of the European salmon its marine aspect are entirely wanting here. Not a single specimen of Agamonema was discovered, although two species are found in the European salmon, and one of them, Agamonema capsularia, is very common. Both Ascaris and Echinorhynchus are unrepresented in the parasitic fauna of the Sebago salmon. Among the numerous species of each already recorded as parasitic in the European salmon three out of four are purely marine. Here again one notes that the marine elements in the parasitic fauna of the European salmon are wanting in the Sebago salmon. Possibly the large filariad found abun- dantly in the Alaska salmon, and reported also from one or two salmon taken in Sebago Lake, forms an exception to the general rule. As I have already noted, it appears to be marine in origin. This may be, however, a false argument, and the species may actually be one limited to this host or to the salmonid family, regardless of habitat. In this connection one naturally recalls at once the case of Abothrium crassjiin, which, from the observations on salmon in the North Sea and then in the Rhine, might be said to be a marine form, since it gradually disappears on the journey up the Rhine. But it occurs in hosts of purely fresh-water habitat, such as Salmo hucho in Europe and Cristivomer namaycush in the Great Lakes of North America. Evidently further informa- tion is needed before one can safely assign this nematode to a definite habitat. Summing up all the evidence concerning the parasites of the Sebago salmon, one finds that four species are unknown in character, one only is possibly marine, •one is a pure salmon parasite, and three are clearly fresh-water forms. The latter are also its most frequent and numerous guests. Furthermore, the Sebago salmon lacks every one of those parasites found in the European salmon which must be regarded as purely or largely marine, and possesses in common with its European congener only one characteristic salmon parasite and possibly also two fresh-water forms, which, though abundant in its own parasitic fauna, are very rare in that of its relative. The parasitic fauna of the Sebago salmon manifests a striking fresh-water aspect, all the more unexpected in view of the marine character of that in the European salmon as demonstrated by Zschokke. One could hardly find a more convincing demonstration of the fundamental biological relation between parasite and host. The parasitic fauna of any animal is primarily a function of its habitat. 1 192 BULLETIN OF THE BUREAU OF FISHERIES. BIBLIOGRAPHY. Bean, T. H. i8go. Report on the salmon and salmon rivers of Alaska, with notes on the conditions, methods, and needs of the salmon fisheries. Bulletin U. S. Fish Commission, vol. x, p. 165-208. 1893. Life history of the salmon. Bulletin LI. S. Fish Commission, vol. xiii, p. 21-38. Bellingham, O. 1840. Catalogue of the Entozoa indigenous to Ireland. Magazine of Natural History, n. s., vol. 4. P- 343-351- 1844. Catalogue of the Entozoa indigenous to Ireland. (Reprinted.) Annals and Magazine of Natural History, vol. 14, p. 471-479. 1844. On Irish Entozoa. Ibid., vol. 13, p. 167-174, 422-430; vol. 14, p. 162-165, 251-256. Braun, M. 1890. Notiz uber Auswanderung von Distomen. Centralblatt fiir Bakteriologie und Parasiten- kunde, bd. 7, p. 568. 1894. Vermes. -Trematodes. Bronn's Klassen und Ordnungen des Thierreichs, bd. iv, abt. i. DlESING, C. M. 1851. Systeraa Helminthum, vol. II. Vindobonse. Drummond, J. L. 1838. Notices of Irish Entozoa. Magazine of Natural History, n. s., vol. 2, p. 515-524, 571-577 655-662, 32 fig. GoEZE, J. A. E. 1782. Yersuch einer Naturgeschichte der Eingeweidewiirmer thierischer Korper. 471 p., 35 pi. Blankenburg. Hausmann, L. 1897. Ueber Trematoden der Siisswasserfische. Revue Suisse de Zoologie, t. 5, p. 1-42, i pi. HoEK, P. P. C. 1899. Neuere Lachs- und Maifisch-Studien. Tijdschrift der Nederlandsche Dierkundige Vereeni- ging, 2 de serie, deel vi, p 156-242, 5 pi. Jordan, D. S., and Evermann, B. W. i8g6. The fishes of North and Middle America. Bulletin 47, V. S. National Museum, pt. i. 4 Leidv, J. 1 85 1. Contributions to helminthology. Proceedings Academy of Natural Science, Philadelphia, vol. 5, p. 205-210. 1871. Notices of some worms, Dibothrium cordicefa, Hirudo, Gordius. Ibid., vol. it,, p. 305-307. LiNSTOW, O. von 1878. Compendium der Helminthologie. Hannover. " 1889. Compendium der Helminthologie. Nachtrag. Hannover. Looss, A. 1899. VVeitere Beitrage zur Kenntniss der Trematoden-Fauna Aegyptens, zugleich Versuch einer naturlichen Gliederung des Genus Diilomum Retzius. Zoologische Jahrbiicher, Syst., bd. 12, p. 521-784, 9 taf. 1894. Die Distomen imserer Fische und Frosche. Bibliotheca Zoologica, hft. 16. 1907. Beitrage zur Systematik der Distomen — Zur Kenntniss der Familie Hemiurida;. Zoologische Jahrbiicher, Systematik, bd. 26, p. 63-180, 9 taf. INTERNAL PARASITES OF THE SEBAGO SALMON. II 93 LtJHE, M. 1899. Zur Anatomie und Systematik der Bothriocephaliden. Verhandlungen der deutschen zoologischen Gesellschaft, 1899, p. 30-55. 1901. Ueber Hemiuriden. Zoologischer Anzeiger, bd. 24, p. 394-403, 473-488, 3 fig. McIntosh, W. C. 1863. Notes on the food and parasites of the Salmo salar of the Tay. Journal Linnean Society of London, vol. 7, p. 145-154. MoNiEz, R. 1881. M^moires sur les Cestodes. i. Travaux de I'lnstitut zoologique Lille, t. 3, fasc. 2, 238 p., 12 pi. MtJHLINr,, P. 1898. Die Helminthen-Fauna der Wirbeltiere Ostpreussens. Archiv fiir Naturgeschichte, 1898, p. i-i 18, 4 taf. MOllER, O. F. 1776. Zoologiae danicae prodromus seu animalium Daniae et Norvegiae indigenarum characteres, nomina et synonytna imprimis popularium Havnise 1776. (Cited after Braun, 1894.) 1777. Zoologia danica seu animalium Daniae et Norvegiae rariorum ac minus notorum descrip- tiones et historia. 4 vol. Havniae. (First edition said to be 1777; that consulted was 1788-1806.) 1780. Cm Baendelorme (Nye saral. af det Kgl. Danske Yidensk. Selsk. Skrift. Forste deel, Kopenhavn, 1781, p. 55. Deutsch ira: Naturforscher St. xiv. Halle, 1780, p. 129). (Cited after Braun, 1894.) Odhner, Th. 1905. Die Trematoden des arktischen Gebietes. Fauna Arctica, bd. 4, p. 291-372, 3 taf. OUSSON, P. 1867. Entozoa, iakttagna hos Skandinaviska hafsfiskar. Platyelminthes. Lund's Universitets Arsskrift, 3:1-59, 2 taf. 1876. Bidrag till Skandinaviens Helrainthfauna. i. Kongliga Svenska Vetenskaps Akademiens nya Handlingar, bd. 14, no. i, 35 p., 4 pi. 1893. Bidrag till Skandinaviens Helrainthfauna. 11. Ibid., bd. 25, no. 12, 41 p., 5 pi. Pratt, H. S. 1902. Synopses of North American invertebrates, xii. The trematodes. Part 11. The Aspi- docotylea and the Malacocotylea, or Digenetic Forms. American Naturalist, vol. 36, p. 887-971. RUDOLPHI, C, A. 1809. Entozoorum, sive vermium intestinalium historia naturalis, vol. 11, pt. i. Amstelsdami. 1810. Entozoorum, sive vermium intestinalium historia naturalis, vol. 11, pt. 2. Amstelsdami. 1819. Entozoorum synopsis. Berolini. Rutter, C, 1902. Natural history of the quinnat salmon. A report of investigations in the Sacramento River 1896-1901. Bulletin U. S. Fish Commission, vol. xxn, p. 67-143. Schneider, G. 1902. Ichthyologische Beitrage. iii. Ueber die in den Fischen des Finnischen Meerbusens vor- kommenden Endoparasiten. Acta Societatis pro Fauna et Flora Fennica, vol. 22, no. 2, p. 1-87. Stafford, J. 1904. Trematodes from Canadian fishes. Zoologischer Anzeiger, bd. 27, p. 481-495. 1 1 94 BULLETIN OF THE BUREAU OF FISHERIES. Stiles, C. W., and Hassall, A. 1894. A preliminary catalogue of the parasites contained in the collections of the United States Bureau of Animal Industry, United States Army Medical Museum, Biological Depart- ment of the University of Pennsylvania (Coll. Leidy) and in Coll. Stiles and Coll. Hassall. Veterinary Magazine, vol. i, p. 245-253, 413-437. Tosh, Jas. R. 1905. On the internal parasites of the Tweed salmon. Annals and Magazine of Natural History, 7 ser., vol. 16, p. 115-119, I pi. ZSCHOKKE, Fr. 1899. Erster Beitrag zur Parasitenfauna von Trutla salar. 'Verhandlungen der Naturforschenden ■ Gesellschaft in Basel, bd. 8, p. 761-795, pi. 11. 1890. Ueber Bothriocephalenlarven in Trutla salar. Centralblatt fur Bakteriologie und Para- sitenkunde, bd. 7, p. 393-396, 435-439, 5 fig. 1891. Die Parasitenfauna von Trutla salar. Ibid., bd. 10, |). 694-699, 738-745, 792-801, 829-838, 8 tab. 1896. Zur Faunistik der parasitischen Wiirmer von Siisswasserfischen. Ibid., bd. 19, p. 772-784, 815-825. 1902. Marine Schmarotzer in Siisswasserfischen. Verhandlungen der Naturforschenden Gesell- schaft in Basel, bd. 16, p. 1 18-157. EXPLANATION OF PLATE. Fig. I. Azygia sehago. Group of individuals from Salmo sehago, after preservation in corrosive sub- limate and then alcohol. X2. 2. Azygia sehago. Specimen from salmon, stained and mounted in balsam. Dorsal view. Xi2>^. 3. Azygia sehago. Anterior region of alimentary canal in lateral aspect. Reconstruction by Messrs. W. M. Anderson and H. B Boyden. in, intestine; ce, oesophagus; as, oral sucker; ph, pharynx. Highly magnified. 4. Azygia sehago. Longiscction showing relations of principal organs, exc, main excretory vessels; Ipm, longitudinal parenchym muscles, for explanation of which compare text; vit, follicles of vitellarium. Camera drawing. X358. 5. Azygia sehago. Female reproductive system in dorsal aspect. Semidiagrammatic to show relation of organs in ovarial complex. Ic, Laurer's canal; od, germ duct; ov, germarium; sg, shell gland; iit, first coils of uterus; yd, transverse vitelline duct; yr, yolk reservoir. After reconstruction by Messrs. Anderson and Boyden. Highly magnified. 6. Azygia sehago. Transsection through ovarial complex, showing relations of organs to common capsule (see text), in, intestinal crura; Ipm, longitudinal parenchym muscles; ov, germ gland; sg, shell gland; ut, first coil of uterus; vii, follicle of vitellarium; yd, common yolk duct and part of yolk reservoir. Camera drawing X60. 7. Sparganum sehago, nov. sp. Bothriocephalid larva from spleen of Salmo sehago. Drawn from alcoholic specimen. X2. 8. Head of larva, shown in fig. 7 X25. 9. Sparganum sehago, nov. sp. Bothriocephalid larva from body cavity of Salmo sehago. Drawn from alcoholic specimen. X2. 10. Head of larva, shown in fig. 9. X25. BuL. U. S. V,. F., 190.S. Pl.ATK CXXI.