THE INTER-RELATIONSHIPS 
 
 OF 
 
 FLAGELLATA & PRIMITIVE ALG^. 
 
 By frank cavers, D.Sc., F.L.S. 
 
 Lecturer in Botany at Goldsmiths’ College, 
 University of London. 
 
 NEW PHYTOLOGIST REPRINT, No. 7. 
 
 LONDON : 
 WESLEY & SON, 
 ESSEX STREET, STRAND, 
 1913 . 
 
■■ ■ ■ ^ 
 
 : " 31 1 / 
 
 t ' 
 
 I CONTENTS, 
 
 j I. — Introduction... 
 
 I 
 
 ' II.— General Characters of the Flagellata 
 
 III. — Chloromonad^ and Heterokont^ (“ Confervales,” 
 
 “Yellow-Green Alg^ “) 
 
 IV. — Relation of Green Alg^ to Chlamydomonads 
 
 j V. — VOLVOCALES 
 
 ^I* I'he Chrysomonads 
 
 ) 
 
 ^ VI I. -The Cryptohonads and Their Relationships 
 
 Peridiniales (Dinoflagellata) and Their 
 ^ Relationships... 
 
 ( IX. — Conclusion... 
 
 j » " Literature Referred To 
 
 i Addendum... 
 
 
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THE INTER-RELATIONSHIPS OF FLAGELLATA 
 AND PRIMITIVE ALG^. 
 
 By.F. Cavers. 
 
 I — Introduction. 
 
 A lthough the phylogeny of the lower Alg^e has been treated 
 in some detail in various recent works, such as those by 
 Oltmanns (95), Lotsy (89), and West (146), a merely casual 
 perusal of the rapidly increasing literature dealing with these 
 and other lowly organisms suffices to show that even in the 
 most recent general treatises, whether botanical or zoological, 
 there are many gaps — apart from the fact that such text-books of 
 necessity become more or less out-of-date as soon as they have been 
 published. It is perhaps inevitable that botanical writers are 
 inclined to overlook, or at any rate fail to appreciate fully, the 
 researches of zoologists on the vast assemblage of unicellular 
 organisms now conveniently designated as “ Protista,” while the 
 zoologists have perhaps erred in the past by definitely claiming as 
 animals a considerable number of organisms which are regarded 
 by botanists as definitely vegetable in nature despite their possession 
 of certain animal-like characters. 
 
 As is aptly remarked by Willey and Hickson (151) in their 
 recent work on the Mastigophora (Flagellata) in Lankester’s 
 Treatise on Zoology — “ It was formerly a question whether such an 
 order of Mastigophora should be reckoned among the unicellular 
 Algae or among the Protozoa, but this controversy is now practi- 
 cally over, and biological disquisitions upon the group are equally 
 at home in zoological and botanical treatises and journals.” The 
 same view has also been expressed by various other writers, 
 and the study of the Flagellata and other unicellular organisms has 
 within recent years emerged as a distinct and rapidly growing 
 branch of biological investigation — “ Protistology” — though, in the 
 nature of things, its scope is defined very differently by different 
 biologists. In the wide sense, the Protista include all unicellular 
 organisms, whether they be regarded as definitely animal, definitely 
 vegetal, evenly balanced in characters between the two kingdoms, 
 or transitional between the ill-defined Protista (in the narrow sense) 
 on one hand and either of the two main kingdoms on the other. 
 
 It is hoped that the following brief sketch of the possible inter- 
 relationships between certain groups of Flagellata, primitive Algae, 
 and certain groups of Protozoa may be useful to students of both 
 Botany and Zoology, and to this end a tolerably extensive biblio- 
 graphy has been compiled in order to indicate the sources from 
 which the material has been drawn and to which the reader 
 may be referred for details that could not be included in this 
 necessarily condensed summary. 
 
 Just twenty years ago, Klebs (67) published the first compre- 
 hensive work on the Flagellata in which these organisms — usually 
 treated by zoological writers as a division of the Protozoa — were 
 studied in detail from the botanical as well as the zoological point 
 of view. Klebs pointed out that the Flagellata are a hetero- 
 genous assemblage in which, more than in any other Protista, the 
 formal distinctions hitherto drawn between the animal and 
 vegetable kingdoms entirely vanish ; that the Flagellata may 
 be regarded as a central group from which the various classes of 
 
2 Flagellata and Primitive Alga. 
 
 Protozoa have arisen ; and that this group also embraces a number 
 of specialised lines of descent — including several distinct lines 
 leading to the lower Algae. The results of recent work, some of 
 which it is proposed to summarise and discuss here, have in the 
 main confirmed the views expressed by Klebs in his diagrammatic 
 scheme of the phylogenetic relationships between Flagellata and 
 Algae — with certain modifications arising from the discovery of 
 new forms and the reinvestigation of forms whose structure and 
 development had been imperfectly known — and have led to great 
 advances in our knowledge of the phylogeny of the Algae, and to 
 striking changes in the classification of the Green Algae in 
 particular. 
 
 It is now generally recognised that a division of the Flagellata 
 into forms referable to the vegetable kingdom (forms bearing 
 chlorophyll, having a cell-wall of cellulose, and having no mouth 
 or other means for ingesting solid food) and foi ms referable to the 
 animal kingdom (forms without chlorophyll, without a cell-wall or 
 with a wall not consisting of cellulose, and having a mouth or 
 other means for solid ingestion) would be absolutely unnatural and 
 could only be made by ignoring genetic relationships which are 
 perfectly obvious. Moreover, such a division would leave out of 
 account a large number of organisms which could not logically he 
 placed in either division. A better criterion would seem to be 
 afforded by the consideration that in the lowest organisms regarded 
 as animals, somatic growth and reproduction by fission are marked 
 by active mobility, the flagellate cells growing and dividing in this 
 condition ; whereas in the lowest organisms regarded as plants, 
 somatic growth and division are marked by stability, and 
 the flagellate cells do not grow and divide but may conjugate 
 and give rise to a sedentary zygote. We shall see, however, that 
 even this criterion — which has led to the inclusion by zoological 
 writers of the greater part or even the whole of the Flagellata in 
 the animal kingdom as a class of the Protozoa — is vitiated by the 
 occurrence of transitional forms through which certain Flagellate 
 groups shade off almost imperceptibly into definitely Algal 
 organisms. 
 
 Assuming that the lower Algae have arisen from a Flagellate 
 ancestry, the work of the majority of recent writers on the 
 phylogeny of the Algae has been directed towards the tracing of 
 the lines of descent leading from certain Flagellate groups to the 
 lower Algae, and to the formulation of a system of classification 
 which shall reflect the phylogenetic relationships thus disclosed. Of 
 the four main groups into which the Algae have usually been divided, 
 the Blue-green Algae are probably related in some way to the 
 Bacteria, but the origin and affinities of both divisions of “ Schizo- 
 phyta ” are quite uncertain, though they are possibly of Flagellate 
 ancestry ; the Green Algae may be traced, through transitional forms, 
 to at least two distinct sources among the green Flagellata ; the 
 Brown Algae have similarly been shown, especially by quite recent 
 work, to have arisen from certain Flagellata with brown chromato- 
 phores ; while as regards the Red Algae there appears at present 
 to be no better-founded view than that suggested by Klebs — that 
 they may have arisen from Brown Algae. 
 
 In recent speculations concerning the evolution of plants it 
 has generally been assumed that the earliest vegetable organisms 
 possessed chlorophyll and were autotrophic (photosynthetic)) 
 
General Characters of the Flagellata. 3 
 
 forms, their immediate ancestors being autotrophic Flagellates ; 
 that the Green, the Brown, perhaps also the Red, and more 
 doubtfully the Blue-green Algae arose respectively from similarly 
 coloured Flagellata ; and that the various groups of Fungi have 
 arisen independently from different Algal forms — though some 
 fungal series may have come directly from Flagellata, However, 
 Vuillemin (144) has pointed out that in our ignorance concerning 
 the conditions under which the earliest forms of life appeared, we 
 are hardly justified in assuming that photosynthetic organisms 
 necessarily preceded heterotrophic organisms in time, and that 
 from this point of view the nitrogen-fixing Bacteria have as good a 
 claim as chlorophyll-bearing organisms to be regarded as the 
 nearest living representatives of the earliest forms of life. We 
 cannot, however, construct a series of existing forms connecting 
 the Bacteria with the main autotrophic Algal phyla, though it has 
 been suggested (Doflein, 40 ; Zuelzer, 158) that the Bacteria may 
 have given rise, through the Spirochsetes, to the Flagellata. 
 
 Starting from simple coloured autotrophic organisms, 
 Brunnthaler (17) argues that the Red Algae are the most ancient 
 group of plants, on the grounds that (i) the earliest plants were 
 in all probability free-swimming Flagellate forms, and no such 
 forms occur among the present-day Red Algae ; (ii) the red pigment 
 of the Rhodophycese is an adaptation to life in the deeper waters 
 of the sea and in the dim light of the primitive world with its 
 dense cloud canopy, since this pigment absorbs the rays in which 
 that light would be rich ; (iii) the present-day Red Algae show 
 hardly any primitive types, and motile free-swimming reproductive 
 cells 'are absent from the group. The Brown Alg^ would come 
 next ; that this is a younger group is indicated by the great diversity 
 in structure of the reproductive organs, the constant presence of 
 .flagellate reproductive cells, and the adaptation of the brown 
 pigment to the absorption of light more closely approaching in 
 quality that of the bright sunlight reaching the surface of the 
 present world, but still with an atmosphere richer in water vapour 
 than that of to-day. Meanwhile, the primitive Red Algae had 
 become adapted to the dim ancient light, and therefore restricted 
 to the deeper sea, leaving the upper waters as an open field for the 
 evolution of the new brown seaweed population. The Green 
 Algae, finally, are the youngest group to appear in the succession 
 outlined by Brunnthaler, their green colour being an adaptation 
 to the fuller light (richer in the less refrangible rays of the 
 spectrum) of modern times ; the early forms were marine, but 
 after possessing the upper waters of the sea and invading estuaries 
 they became adapted also for life inland in fresh water. According 
 to Brunnthaler, there is no direct relationship between the present- 
 day Algae and Flagellata, though the earlier Flagellates may have 
 given rise to the Red Algae ; the living Flagellata he regards 
 as the termination of an ancient series of organisms which have 
 evolved independently of the Algae. 
 
 II — General Characters of the Flagellata. 
 
 Without dealing further with such questions as these, it may 
 be noted in passing that there is a good deal to be said against the 
 assumption, which has frequently been made, that the Flagellata 
 represent the most primitive of known organisms ; this claim may 
 
4 
 
 Flagellata and Primitive Algce. 
 
 perhaps quite as reasonably be put forward for bacterial forms or 
 for the simpler amoeboid types of Protozoa. For instance, there 
 are grounds for regarding a flagellum as a specialised type of 
 pseudopodium, since between the blunt pseudopodium of an Amceha 
 and the vibratile flagellum of a typical Flagellate there are various 
 intermediate forms of protoplasmic outgrowth concerned in loco- 
 motion or ingestion of food or other functions. In any case, how- 
 ever, the Flagellata appear to include forms leading by a series of 
 transitional types to the lower Green and Brown Algae, and these 
 are our chief concern here. 
 
 The characters given by Klebs as distinguishing the Flagellata 
 from the motile unicellular Green Algae — the Chlamydomonads, 
 which are still included by zoological writers in the Flagellata 
 under the name “ Phytoflagellata ” — may be enumerated as 
 follows. Body unicellular or a colony of cells, cell uninucleate 
 with a thick or thin external layer of protoplasm — the periplast — 
 in which amoeboid chnages of form may take place. Outside this 
 a non-living investment of the cell is frequently present, of varied 
 form and often not closely adherent to the body. Specialised 
 anterior end of clear protoplasm bearing one or more flagella. 
 Organism always remaining capable of movement. Nutrition 
 either holozoic (solid food being taken by pseudopodia, through a 
 specialised mouth, or otherwise), saprophytic, or holophytic. In the 
 last case the chromatophores are green or yellow-brown, and may 
 take the form of bands, plates, or discs. IVne pyrenoids entirely 
 absent. Paramylum, leucosin, or a fatty oil the visible anabolites 
 (products of assimilation). Starch entirely absent. Reproduction 
 by simple longitmluial fission, usually beginning at the anterior end 
 of the body. Individual always capable of forming resting cysts. 
 Gamogenesis apparently entirely absent. 
 
 It may be noted that recent work has made it extremely 
 difficult to frame a definition of the Flagellata which shall separate 
 this group sharply from the Protozoa on one hand and the lower, 
 Algae on the other. Exceptions have to be admitted in connexion 
 with almost every character hitherto given in definitions of the 
 group. The body usually has a definite anterior end from which 
 one or more flagella arise, but in Mnlticilia the numerous flagella 
 spring from various points of the spherical body ; the flagella are 
 usually motile and unbi anched organs, but in certain Chrysomonads 
 they are non-motile and even branched, corresponding with the 
 pseudopodia of various Protozoa j the visible product of anabolism 
 is usually either oil or leucosin or paramylum, but starch is formed^^ 
 in certain Chrysomonadineae (e.g., Cryptomonas) and in the Polyble-g 
 pharidaceae (if these be regarded as Flagellates rather than Chlamy-j. 
 domonadine Algae) ; the great majority are uninucleate, but thcg 
 Trypanosomes have two nuclei, while Multicilia lacustris is describe-^ 
 as having a large number; as a rule, division is longitudinal anc . 
 occurs in the motile phase, but it is sometimes transverse (e.g.* 
 Oxyrrhis, Sty lochry salts) and it may occur exclusively in a resting 
 state ; sexual reproduction is usually absent, but a sexual process 
 has been shown to occur in various genera belonging to different 
 groups of Flagellata (39, 50, 118, 121). 
 
 In Senn’s account (135), which was published in 1900, the Fla- 
 gellata fall into seven divisions. Three of these comprise only colour- 
 
General Characters of the Flagellata. 5 
 
 less heterotrophic forms (with holozoic, saprophytic, or parasitic 
 nutrition), while the members of the remaining four divisions are 
 normally provided with pigments which make holophytic nutrition 
 possible, though many of these are also capable of heterotrophic 
 nutrition and may therefore be described as “ mixotrophic.” In the 
 lowest of the colourless groups in Senn’s arrangement, the Panto- 
 stomatineae, any portion of the body can ingest solid food by means 
 of pseudopodia, while in all the remaining forms capable of holozoic 
 nutrition such ingestion occurs only at certain definite points; the 
 Pantostomatinean genus Multicilia has a spherical protoplast with 
 numerous radially arranged flagella, but in all other Flagellata 
 the body shows radial or bilateral symmetry, or may be asymmetrical, 
 and the number of flagella is more limited. According to Senn, the 
 Pantostomatineae have given rise to the lower Protozoa (Sarcodina); 
 to the small Flagellate group Distomatineae with irregular bilateral 
 symmetry and paired groups of flagella — this group forming a 
 blindly-ending line ; and to the very large group Protomastigineae 
 which comprises about half of the known genera of Flagellata and 
 shows great variety in form and structure. The Protomastigineae 
 may be regarded as the common source of the Infusoria, Mycetozoa, 
 Sporozoa, and perhaps also the Bacteria, on one hand, and of the 
 four groups of pigment-bearing or “ Algal ” Flagellata on the other. 
 Of these latter, the Chrysomonadinea? and the Cryptomonadineae 
 are, according to Senn, closely related but of independent origin ; 
 the. Chrysomonadineae have brown chromatophores, produce oil and 
 leucosin, and show affinities with the Brown Algae and the Diatoms, 
 while the Cryptomonadineae produce starch, are variously coloured 
 or in some cases colourless, and may have given rise to the Peri- 
 diniales and the Green Algae. The two remaining groups, Chloro- 
 monadineae and Euglenineas, differ from the other groups in having 
 numerous green chromatophores ; there is a more definite periplast 
 or firm outer protoplasmic layer ; the contractile vacuoles are so 
 situated and co-ordinated as to form a pulsating system opening at 
 a definite point on the exterior ; the product of assimilation is oil 
 (Chloromonadineae) or paramylum (Euglenineae). In the Chloro- 
 monadineae, which Senn derives from Monas- and Bodo-Wko. forms 
 among the Protomastigineae, the contractile vacuoles are aggregated 
 at the anterior end of the cell and open to the exterior by a pore. 
 Senn regards the Chloromonadineae as being too highly organised 
 to serve as the starting-point for an Algal group as suggested by 
 Luther and others (see below); but they have by further elaboration 
 of the cell given rise to the Euglenineae, a blindly-ending line repre- 
 senting the highest type of organisation found in the Flagellata and 
 decidedly showing no Algal affinities, whatever may be said of the 
 Chloromonadineae. The Euglenineae have, as compared with the 
 Chloromonads, a more definite, often striated, and highly resistant 
 periplast, and a gullet-like canal leading to a deep-seated vacuole 
 into which a system of small and actively contractile vacuoles is 
 drained. 
 
 Apart from Senn’s compilation, the more comprehensive 
 accounts of the Flagellata are contained in zoological works (18, 
 19, 37, 40, 93, 139, 151), and much of the recent literature on the 
 “ Algal ” forms is published in zoological journals. The Peridiniales 
 will be dealt with in this review, since this group includes decidedly 
 Flagellate forms, and reference will also be made to certain other 
 
6 
 
 Flagellata and Primitive Alga. 
 
 groups {e.g., Cystoflagellata, Silicoflagellata, Coccolithophoridae) 
 not classed by Senn among the Flagellata, though they occupy 
 this position in zoological systems of classification. On the hand, 
 the Trypanosomes and the majority of the other specialised or hete- 
 rotrophic Flagellata need not be considered in a discussion of the 
 origin of Algae from Flagellata. 
 
 In the following pages, it is proposed, taking as a starting- 
 point the treatment of Algal groups in Engler and Prantl’s Pflan- 
 zenfamilien and that of the Flagellata in the same work and in the 
 more comprehensive zoological treatises, to review briefly the 
 advances that have recently been made in our knowledge of certain 
 lines of descent leading from Flagellata through transitional forms 
 to the simpler Algae. Restricting our speculations to such series 
 as appear to include what may he fairly considered as transitional 
 forms, we can recognise three main lines, leading (i) from the 
 simpler Chloromonads to the Heterokontae or Yellow-green Algae; 
 (ii) from the Polyhlepharids to the Chlamydomonads and thence 
 to the Isokontae and other Green Algae ; and (iii) from the Chryso- 
 monads and Cryptomonads to the Brown Algse, the Peridiniales, 
 and probably certain other groups. 
 
 Ill — Chloromonads and Heterokont^ (“ Confervales,” 
 “Yellow-Green Alg/E ”). 
 
 Until recently the Green Algae have usually been divided into 
 Conjugatae, Protococcoideae, Confervoideae, and Siphoneae — the 
 division made, for instance, by Wille in Engler and Prantl’s 
 Piianzenfamilien in 1890, and adhered to, with slight modifications, 
 in that writer’s recent supplement on the Chlorophyceae in the same 
 work (150). The Conjugatae form a natural group, marked by the 
 absence of ciliated reproductive cells — whence the name Akontae 
 given to the group in the modern system of Green Algae based in 
 part upon the ciliation of the asexual reproductive cells or zoogo- 
 nidia — and by the siphonogamic sexual process of conjugation by 
 means of a tube formed by the fusion of processes from the two 
 gametangia. The limits and arrangement of the three remaining 
 classes have, however, been considerably modified, owing chiefly to 
 considerations advanced in publications by Chodat, Bohlin, Luther, 
 and Blackman. 
 
 In all Green Algae excepting the Conjugatae (Akontae), the 
 zoogonidia and zoogametes are typically pear-shaped cells bearing 
 at the anterior end a number of flagella. In most cases there are 
 two (occasionally four) flagella of equal length inserted at the same 
 point (Isokontae) ; in the small order OEdogoniales the motile cells 
 have a circlet of numerous flagella (Stephanokont^) ; while in the 
 Confervales there are two flagella of unequal length (Heterokontae) — 
 in some forms the shorter flagellum may, apparently, be absent.i 
 It may be added that in the attempts that have been made to' 
 connect Algal series with corresponding Flagellate series, the 
 number and insertion of the flagella are not the sole criteria used, 
 various other characters being taken into account. In ceitain 
 groups of Flagellata, e.g., the Euglenineae, the flagella show con- 
 siderable differences in genera which are obviously related closel> 
 to each other as judged by other cytological characters. When due 
 attention is paid to the tout ensemble of characters, how^ever, there 
 can be little doubt that the flagellum characters (numbei*, insertion, 
 
Chloromonads and H eterokontce. 
 
 i 
 
 relative length where two or more are present) may afford a valuable 
 clue to affinities. 
 
 In 1899, Luther (90) described a new genus, Chlorosaccus (Pig. 
 
 Fig. 1. CHLOROMONADINE.(E (Flagellate and Transitional Heterokontas). 
 A to C, Chlonwiosba heteromorpha Bohl. : A, a normal green individual, with 
 nucleus, contractile vacuole, three chromatophores, and oil-drops ; B, resting 
 ,cyst ; C, amoeboid colourless individual. D, E, Vacuolavia vivescens Cienk. : 
 E shows the anterior end more highly magnified, with two vacuoles and in- 
 sertion of flagella in the gullet-like pit. F, Vacuolavia flagellata Senn. G, H, 
 Chlorosaccus fluidus Vuthe.v \ G, portion of a colony; H, motile cell. J to V, 
 Leuvenia natans Gardner ; J, a portion of the floating colony ; K, the same more 
 highly magnified ; L, a motile cell soon after being set free; M, N, O, P, later 
 stages showing amoeboid habit of the zoogonidia ; Q and R, zoogonidia with 
 four and eight chromatophores respectively ; S, resting zoogonidium with the 
 \ flagella withdrawn and with a cell-wall developed; a free floating colony 
 showing the rapidly dividing chromatophores held together by protoplasmic 
 threads ; U,,an earlier stage in development of colony, showing the ruptured 
 cyst-wall at base ; V, section through a young colony showing the nuclei and 
 the chromatophores in pairs. 
 
 A— C from Bohlin ; D, E, from Senn ; F, from Stokes ; G, H, front 
 Luther ; J — V, from Gardner. 
 
8 
 
 Flagellata and Primitive Algce. 
 
 1, G, H), which is of great importance as forming a connecting link 
 between the Chloromonad genus Chloramceha (Fig. 1, A — C) on one 
 hand and the Algal group “ Confervales” on the other. This group 
 had been previously founded as a distinct series of Green Algae as 
 the result of the work of Borzi (14, 15) and of Bohlin (10) on various 
 genera which had formerly been included in the old groups of 
 Protococcoideae, Confervoideae, and Siphoneae. These genera 
 differ from other Green Algae in several characters besides the 
 possession by the motile cells of two unequal flagella — namely, the 
 presence of a large proportion of xanthophyll or carotin in their 
 chromatophores (hence the name “Yellow-green Algae” has been 
 given to the group) which are typically numerous and discoid ; the 
 production of oil instead of starch as the visible anabolite ; and 
 the curious structure of the cell-wall in some genera, e.g., the 
 unicellular Ophiocytium in which the upper part of the wall 
 becomes detached like a lid, and the filamentous Triboimna in 
 which each cell is hounded by the halves of two H -shaped pieces 
 and the whole filament readily breaks up into fragments of this 
 shape. Luther and Bohlin concluded that these forms had arisen 
 independently of the remaining Green Algse, from the simpler 
 types of the Flagellate group Chk)romonadineae, e.g., CliloranKxha, 
 through a transitional form like Clilorosaccus. On the other hand, 
 Chlorambcsa leads through forms like Vacuolaria (Fig. 1, D — F) to 
 the more specialised Chloromonadineie and doubtless to the 
 Euglenineae, which need not be further considered here. 
 
 The genus Leuvenia (Fig. 1, J to V), recently described by 
 Gardner (48), appears to be related to CJilorosnccits and to form 
 an interesting additional link in the chain connecting CJiloramceba 
 with the “ Convervales.” The motile cells are at first pear-shaped, 
 with two unequal flagella and two ovoid curved green chromato- 
 phores (sometimes becoming four or eight by division) ; later the 
 cell becomes amoeboid. Growth occurs in a resting condition — the 
 motile cells come to rest, float to the surface of the water, become 
 spherical, withdraw their flagella, and grow rapidly in size ; then 
 the nucleus divides into as many as twenty, the chromatophores 
 divide by constriction, and finally the whole interior divides up into; 
 zoogonidia, each appropriating two chromatophores and a nucleus. 
 Under certain conditions the resting cells secrete a gelatinous 
 substance causing them to adhere together in stringy floating 
 masses, in which they become spherical; and in this palmella. 
 stage division into zoogonidia occurs as in the ordinary growth^ 
 stage. 
 
 Pascher(112) has recently described a new genus of Hetero- 
 kontse (Pseudotetraedron, which superficially resembles the Proto- 
 coccaceous genus Tetraedron but shows characteristic Heterokontan 
 features — numerous discoid yellow-green chromatophores, pro- 
 duction of oil instead of starch, cell-wall consisting of two portions 
 fitting upon each other like a box and its lid. 
 
 Adopting the terminology suggested by Pascher (1 13), the 
 following arrangement of the Heterokontae may be proposed. It 
 will be noted that the group is hei*e divided into a series of orders 
 which show a striking parallelism with the corresponding divisions 
 of the Isokont^e. The genera of the Isokontan groups are omitted. 
 
Chloromonads and Heterokontce. 
 
 9 
 
 HETEROKONT^. 
 
 ISOKONT/E. 
 
 Hkterochloridales. 
 
 Chloramaozha. 
 
 Stipitococcus. 
 
 VOLVOCALES. 
 
 Heterocapsales. 
 Heterocapsacese. 
 Lenvenia (?) 
 Clilorosaccus. 
 Racovitziella. 
 
 TliTRASPOK'ALES. 
 
 Botryococcacere. \ 
 Botryococciis. r,^x 
 Askeiiasyella. P*' 
 Oodesmits. ) 
 
 
 Mischococcaceae. 
 
 Mischococcus. 
 
 
 H ETEROCOCCALES. 
 
 Chlorobotrydacefe. 
 
 Protococcaliis. 
 
 Chloroboti’ydeiis. 
 Chlorohotrys. 
 Botrydiopsis. 
 Polychloris. 
 Centritractiis, 
 Pseiidotetmedron . 
 Merin^osphcera (?) 
 Bohliiiia (?) 
 
 
 Cblorothecieae. 
 
 Clilorotheciitm. 
 
 Characiopsis. 
 
 Peroniella. 
 
 
 Sciadiaceae. 
 
 Ophiocytinm. 
 
 
 Heterotrichales. 
 
 Tribonemaceae. 
 
 Trihonema. 
 
 Biiniilleria. 
 
 M onocilia. 
 
 Ulotrichales. 
 
 Heterosiphonales. 
 
 Botrydiaceae. 
 
 Botrydiiim, 
 
 Vaucheriaceae. j 
 
 V ancheria. ! (?) 
 
 Dichotomosiphon . ) 
 
 SiPHONALES. 
 
 I 
 
to 
 
 Flagellata and Primitive Algcc» 
 
 IV. — Relation of Green Alg^ to Chla.mydomonads. 
 
 T here appears to be strong support for the view that the 
 majority of the Green Algae may be derived from Flagellate 
 ancestors with two or more equal flagella. In 1897, Chodat (24) 
 pointed out that in the life-history of the lower Green Algae there 
 may be distinguished three conditions, either of which may become 
 dominant, the other two being then transient or suppressed : (i) the 
 zoospore condition or motile stage ; (ii) the sporangium condition 
 or unicellular motionless stage ; (iii) the palmelloid condition, in 
 which non-motile cells are connected into aggregates by cell-walls 
 at right angles to each other. In 1900, Blackman (6) published an 
 important paper on the phylogeny of the Algae, containing not 
 merely a critical summary of modern work bearing upon the 
 problem, but also various far-reaching suggestions as to the lines 
 along which the evolution of the different Algal groups may be 
 traced from Flagellata. Blackman pointed out that among the 
 simple Green Algae which constitute the group of Protococcoideae 
 three divergent vegetative tendencies are observed : (i) a Volvocine 
 tendency towards the aggregation of motile vegetative cells into 
 gradually larger and more specialised motile coenobia ; (ii) a Tetra- 
 sporine tendency towards the formation of aggregations by the 
 juxtaposition of the products of septate vegetative cell-division to 
 form non-motile organisms of increasing definiteness and solidarity; 
 (iii) an Endosphaerine tendency towards the reduction of vegetative 
 division and septate cell-formation to a minimum. The simplest 
 forms showing any one of these tendencies seem clearly to diverge 
 from species of the genus Chlamydouionas, which may be regarded 
 as the phylogenetic starting-point of the various lines of Green 
 Algal descent. The line arising from the Volvocine tendency leads 
 to the Volvocales and culminates in Volvox; the outcome of the 
 Endosphaerine tendency is seen in the Siphoneas ; while the Tetra- 
 sporine line has given rise to the great majority of the Green Algae 
 and through these to the Archegoniatse and other higher plants. 
 
 The phylogeny of the Conjugatae, CEdogoniales, and a few other 
 isolated groups of filamentous Green Algae remains in some doubt, 
 owing to the absence of practicable transitional forms connecting 
 these groups with either the Tetrasporine line on one hand or with 
 distinct Flagellate ancestors on the other. For further details 
 regarding the phylogeny of the Green Algae, reference should be 
 made to the paper by Blackman already mentioned (6), and to the 
 
Relation of Green Algce to Chlamydomonads. 
 
 i I 
 
 classification based by Blackman and Tansley (7) upon the principles 
 set forth in that paper ; also to the systematic works on Algae by 
 Oltmanns (95), West (146), and Lotsy (89), in which due prominence 
 is given to modern views of Algal phylogeny. More recently, 
 Fritsch (46) has published a valuable paper, in which is included a 
 useful bibliography; while Pavillard (115) has contributed a resume 
 of some modern work on Vegetable Protistology — though his “revue 
 rapide ” omits entirely the Brown Flagellata and lower Brown 
 Algae, on which some remarkably interesting work has been published 
 during the last few years. 
 
 The relationships of the three lines of Flagellate-Algal descent 
 here suggested are indicated in the accompanying Table A, a fuller 
 explanation of which will be given later. 
 
 Archegoniatae 
 
 Table A. — Suggested Phylogeny of (I) the Polyblepharid and Chlamydo- 
 monad, (II) the Chloromonad, and (III) the Chiysomonad and Cryptomonad 
 lines. For details see text. 
 
 Since 1900, perhaps the greatest advances in the study of those 
 Flagellates which are more obviously important in connexion with 
 the phylogeny of the Algae have been made among the Chrysomonads 
 and Cryptomonads, but before dealing with these we may consider 
 some interesting additions to our knowledge of the group of Green 
 Algae whose evolution from the Flagellata has, on the whole, been 
 most completely worked out — namely, the Volvocales, using this 
 name to include the entire series of organisms (the “ Phyto- 
 flagellata ” of various zoological writers) representing the transition 
 from Flagellate ancestors to the motile unicellular Green Algas 
 (Chlamydomonads) and the outcome of the Volvocine tendency 
 which leads to the formation of increasingly complex motile 
 coenobia and culminates in Volvox. 
 
Plagellata and Primitive Algce, 
 
 
 V. — VOLVOCALBS. 
 
 The Polyblepharidaceas are included in the Volvocales hy 
 Blackman and Tansley (7), Wille (150), and various other writers, 
 though Fritsch (46) regards them as still belonging to the Flagellata, 
 but it appears quite immaterial how this family is placed in a formal 
 scheme of classification, so long as it is recognised that no sharp 
 line of division separates the Flagellata from the lower Alg^e and 
 that this remarkable transitional family shows an extraordinarily 
 even balance between the two groups. The Polyblepharids agree 
 with typical Flagellates in being devoid of a definite cellulose wall 
 and in undergoing longitudinal division in the motile phase — but it 
 should be noted that in several genera of Volvocales {Chlorogoniuni, 
 Brachiomonas, and even colonial genera like Gonium and the 
 oogamous Eudovina) division may occur while the flagella are still 
 motile. The Polyblepharids have the characteristic basin-shaped 
 Volvocine chromatophore and a pyrenoid, but — as will appear 
 later — the Cryptomonads and some of the other Chrysomonadineae 
 would have as much right to a position among the Algae as have 
 the Polyblepharids if the possession of Algal chromatophores, 
 pyrenoids, starch, and a firm periplast allowing of only slight 
 changes of shape be taken as definitely Algal characters ; while, on 
 the other hand, the fact that sexual reproduction occurs in a Poly- 
 blepharid (Diinaliella) cannot now be regarded as an argument 
 against the reference of this family to Flagellata rather than to 
 Algae. ( 
 
 Probably the most primitive genus of Polyblepharidaceae is 
 Polyhlepharis (Fig. 2, A), in which the broader anterior end of the 
 conical body bears from six to eight flagella in a tuft; in Pyvaniinionas 
 (Griffiths, 52; Fig. 2, B, C) there are four flagella arising from a 
 depression at this end, which is four-lobed, as is also the chromato- 
 phore; in CJdovaster {P\g. 2, D) there is a central fifth flagellum; 
 while in Tetvatotna, a somewhat doubtful and incompletely known 
 form, there are four flagella inserted at separate points on the 
 anterior half of the spherical body. The genus Diuialiella (Fig. 2, 
 E to L), recently described by Hamburger (53) and by Teodoresco 
 (140, 141), evidently forms a transition from the Polyblepharidaceae 
 to the Chlamydomonads, since it has only two flagella and shows 
 conjugation of isogamous zoogametes; while Stephanoptera, recently 
 discovered by Dangeard (35), resembles Pymminionas in structure 
 but has only two flagella, thus connecting Pymminionas with Duna- 
 liella — according to Dangeard, the life-cycle of Stephanoptera ends 
 in encystment, the cyst having sometimes two nuclei instead of one, 
 but the fate of the cyst was not determined. To the Polyble- 
 pharidaceae probably also belongs the genus Chlorodendron (Fig. 2, 
 M to B), placed by Oltmanns (95) in a special family (Chloroden- 
 draceae), with the closely related, or perhaps congeneric, forms 
 Prasinocladus luhricus Kuckuck and Englenopsis subsalsa Davis — 
 these have recently been investigated by Dangeard (34, 36) who 
 regards these forms as being closely related to the Carteriaceae 
 (see below). In the Chlorodendreae, branching colonies are produced 
 by the localised secretion of mucilage derived from the periplast, or 
 cell-wall, of the dividing cells, and this family, or sub-family, forms 
 
Volvocales. 13 
 
 an interesting^ side-line of colonial development arising from a 
 Pyramimonas-Vike type. 
 
 Fig. 2. POLYBLEPHARIDACE^.— A, Polyblepharis singularis Dang. 
 B, C, Fyramhnonas delicatuliis Griffiths : C, anterior view showing extremities 
 of lobes of chromatophore. D, Chloraster gynvis Ehrb., showing stigma or 
 “ eye spot.” E to L, Dunaliella salina (Dun.) Teodor. : E, vegetative cell, with 
 bell shaped chromatophore, large nucleus, and reticulate protoplasm ; F, G, H, 
 stages in division ; J, conjugation of zoogametes ; K, zygospore ; L, rupture 
 of zygospore to set free the zoospores. M to P, Chlorodendyon lubricum (Kuck.; 
 Senn : M, a portion of a colony ; N, a single cell of same ; O, division of cell ; 
 P, motile cell or zoogonidium. A from Dangeard ; B, C, from Griffiths ; D) 
 from Stein ; E and J, fi’om Hamburger; F, G, H, K, L, from Teodoresco , 
 M to P, from Kuckuck. 
 
 In setting forth a new classification of the Volvocales, Pascher 
 (108) has adopted the suggestions made by Oltmanns as to the 
 affinities between Carteria and Spondylomorum, and by Schmidle 
 as to those between Splicerella and Stephanosphcera, and has separated 
 these genera from the remaining Volvocales, dividing this order into 
 the four families, Polyblepharidaceae, Carteriacese, Sphaerellacese, 
 and Chlamydomonadaceas. Wollenweber (153) has suggested that 
 the Volvocine line shows progressive reduction in the number of 
 flagella and of contractile vacuoles, hence Carteria and Sphcerella 
 may be regarded as more primitive than the Chlamydomonads, the 
 former in having four flagella and the latter in having numerous 
 contractile vacuoles (as many as sixty in S. Drcehakensis). It is, 
 however, rather difficult to determine just which cytological 
 characters should be regarded as relatively primitive and which as 
 relatively advanced among the Volvocales. For instance, numerous 
 
14 Flagellata and Primitive Algce. 
 
 contractile vacuoles are found not only in Sphcerella but also in 
 CJilorogoninm (which differs from the Polyblepharids and most of 
 the simpler Chlamydomonads in showing transverse instead of 
 longitudinal division), and in Agloe, a form with somewhat specialized 
 cell structure. Carteria and Spo7idylo)iionn)i agree in having four 
 flagella and in other characters, but though Carteria is usually 
 stated to have a pyrenoid, Jacobsen (61) has described a species 
 (C. ovata) which has none ; according to this writer, Spondylomorum 
 is also without a pyrenoid ; while Chloroiuonas is distinguished from 
 its ally Chhuiiydomonas solely on the ground that it lacks a pyrenoid, 
 but this simply means that systematists have described pyrenoidless 
 species or even varieties (Serbinow, 137) of Chlamydomoiias as 
 belonging to a distinct genus — on other grounds, there is little 
 doubt that CJdamydonionas and CJdoronionas are quite unnatural 
 genera, and will probably have to be revised and split up as the 
 result of further investigations. Most of the Volvocales have a 
 single pyrenoid, but in Chlamydoinonas inhcerens (Bachmann, 3) 
 two or three of these bodies may be present, while in C. coccifera 
 (Goroschankin, 51, iii) there are five to eight pyrenoids ; two occur 
 in Sphcerella Drcebakeusis and in Steplianosphcera, while Sphcerella 
 pluvialis, ChlorogoniufH, and Pleodorina have a large number of 
 pyrenoids. 
 
 Fig. 3. CARTERIACE.<E. — A, Carteria ovata Jacobsen : this species has 
 no pyrenoid , the chromatophore contains numerous small starch grains. 
 B, C, Scherjfelia phacus Pascher : C shows the cell cut across, to make clearer 
 the wing-like expansion of the cell-wall and the structui'e of the U-shaped 
 chromatophore. D to G, Spondylomorum quaternarium Ehrb. : D, a normal 
 
 sixteen-celled coenobium ; E, an eight celled coenobium ; F, division of each 
 cell to form a daughter coenobium ; G, daughter coenobium not yet set free 
 from mother-cell. A, D to G, from Jacobsen ; B, C, from Pascher. 
 
 The family Carteriaceae includes Carteria (Fig. 3, A), which has 
 a very thin wall ; Scherffelia (Fig. 3, B, C), in which the cell is 
 flattened, oval in outline and slightly biconvex in cross-section, 
 
Volvocales. 
 
 15 
 
 with a thick wall which in one species is produced into a marj^inal 
 wing on either side, two chloroplasts which may or may not be 
 united behind to form a U-shaped structure (obviously derived from 
 splitting of an originally basin-shaped chromatophore), and no 
 pyrenoid ; Tetrablepluiris, a colourless saprophytic form probably 
 derived from Carteria ; and Spondylomonuii (Fig. 3, D to G), a colonial 
 form constructed on a plan quite different from that seen in the 
 coenobial Chlamydomonadace^e and consisting of sixteen Carteria^ 
 like cells in four alternating tiers of four cells each, attached to a 
 gelatinous rod-like axis. Among the Carteriaceae, sexual reproduction 
 is only known in one or two species of Carteria which produce 
 isogamous zoogametes. It is of interest to note that the symbiotic 
 “ Zoochlorella ” found in the Planarian worm Convoluta roscoffensis 
 (Keeble and Gamble, 65) is a species of Carteria ; the single species 
 of Spondylonioruni {S. quaternarhun), hitherto known only from 
 Europe and Asia, has recently been discovered by Campbell (20) 
 in California. 
 
 Apart from the Polyblepharidaceae and Carteriaceas, the 
 Volvocales have a pair of flagella, though a single flagellum occurs 
 in a species of Polytoma (Pascher, 108) and in the genus Mastigo- 
 spheera. The Sphserellaceae, including the unicellular SpJicerella 
 {H cematococcus) and the colonial Stephanosphcera, are distinguished 
 from the remaining Volvocales — the Chlamydomonadacese — mainly 
 by the peculiar structure of the cell-wall. Various contributions 
 to the knowledge of Sphcerella have recently been made, especially 
 by Peebles (116), Reichenow (119), and Wollenweber (152, 153). 
 What has usually been taken for a thin outstanding cell-wall is in 
 reality a firm outer layer, while the supposed sap-containing space 
 between wall and protoplast is a thick inner gelatinous coat, 
 traversed by fine branching pits into which protoplasmic threads 
 extend. Reichenow has minutely studied the structure and mitotic 
 division of the nucleus and the shifting of the originally longitudinal 
 axis of division into an oblique or transverse position. The chloro- 
 plast is a spongy and reticulate structure, and in S. pluvialis there 
 are numerous pyrenoids at the nodes of the network. Though 
 SpJicerella has been so much worked at. Miss Peebles appears to 
 have been the first to observe a sexual process in this genus; she 
 states that when dry encysted cells of 5. pluvialis are moistened 
 and exposed to strong light, the contents of the cyst divide into 
 eight to sixty-four gametes which fuse in pairs, as is also the case 
 in Stephanosphcera, 
 
6 
 
 Flagellata and Primitive Algce. 
 
 O F the unicellular Chlamydomonadaceas, Chlorogonium (Fig. 4, 
 F, G, H) is probably on the whole the most primitive. In its 
 elongated spindle-like form, this genus differs from the majority of 
 the Volvocales, hut an approach to the same shape is seen in 
 Cavteria obtusa, and the zoogametes of Stephanosplicera are spindle- 
 shaped. In Chlorogoninm the cell divides transversely to foi’m a row 
 of four daughter-cells, but these at once become elongated and 
 slide past each other, acquiring the spindle form. Transverse 
 division occurs in some species of Chlainydomonas (Fig. 4, B), 
 though here, as in Sphcerella, division is originally longitudinal and 
 there is rotation of the dividing protoplast. In Chlorogoiiinm the 
 chloroplast is ill-defined and spongy and varies considerably in 
 form, being in some cases ring-like or even spiral, hence sym- 
 metrical halving can he attained without the longitudinal division 
 which is apparently essential in forms with a basin-shaped chloro- 
 plast ; theie are numerous (up to sixty) pyrenoids and about a 
 dozen contractile vacuoles (Jacobsen, 61). Cevcidiiim resembles 
 Chlorogonium, but has only two pyrenoids and two vacuoles. 
 Other simple forms are CJdamydonionas (Fig 4, A to D) and 
 CJdoromonas, the former with pyrenoids (typically one, but some- 
 times more) and the latter with none. Pascher’s new genus Agloe 
 (Fig. 4, E) is allied to these forms, but its chloroplast is peculiar 
 in structure, resembling two conical flasks placed base to base and 
 being H-shaped in optical section, with a pyrenoid in the middle of 
 the transverse plate-like portion, and there are numerous contractile 
 vacuoles. Glceonionas is an imperfectly known genus, probably allied 
 to Chloromonas but with several chloroplasts. Various other genera 
 have been described which probably represent offshoots from the 
 CJilumydomoiKis type, though some of them are imperfectly known. 
 Thus, Coccojnomis (Fig. 4, J, K) appears to differ from Chlainydomonas 
 chiefly in having a greatly thickened wall, often four-angled ; 
 Pteromonas (Fig. 4, L, M) is also thick-walled, the wall projecting 
 as two lateral wings, as in the Carteriaceous genus Scherffelia ; 
 while Phacotns has a sculptured wall consisting of two loosely 
 connected valves which separate to let the daughter-cells escape. 
 Another elaboration is seen in Brachiomonas (Fig. 4, P, Q) and 
 Lohomonas (Fig. 4, M, N) ; in the former the cell has a pointed 
 posterior process and from its rounded anterior end there spring 
 four recurved processes, in the latter the ovoid cell is produced into 
 several rounded wart-like out-growths. In Brachiomonas (Fig. 4, 
 R, S) the daughter-cells acquire the form of the parent before 
 escaping (Teodoresco, 14 0; West, 147); as pointed out by 
 
Volvocales. 
 
 17 
 
 Fig. 4, Chlamydomonadace^. A, B, CJilamydomonas {Chloromonas) 
 variahilis Dang. : this species has no pyrenoid ; C shows transverse division. 
 C, D, Chi. Ehrenbergii Gorosch. (longitudinal division shown in D). E, Agloe 
 biciliata Pascher. F, G, H, Chlorogonium euchlonmi Ehrb : in G the protoplast 
 shows transverse division into two, in H the four daughter-cells formed by a 
 further division have become arranged longitudinally within the mother-cell. 
 J, K, Coccomonas orbicularis Stein : in K the wall of the resting cell has ruptured 
 to set free the four daughter-cells. L, M, Pteromonas alata (Cohn) Seligo ; 
 
 B 
 
i8 
 
 Flagellata and Primitive AlgcB. 
 
 in M the liberation of the four daughter-cells. N, O, Lobomouas Fraucei Dang. 
 P to S. Brachiomonas submarina Bohlin : P and R in side view, Q and S in 
 anterior view ; in R and S the formation of daughter cells. T to V, Platydorina 
 caudata Kofoid : T, surface view ; U, side view, showing the slight spiral twisting 
 of the plate-like coenobium ; V, a single cell. \V, Stephanoon Askenasii Schewk. 
 X, Pleodorina illinoisensis Kofoid (the four small vegetative cells are shown at 
 the left). 
 
 A to D, F to H, from Jacobsen ; E, from Pascher ; J, K, from Stein; L, 
 iM, from ^^■ille ; N, O. from Dangeard : P, Q, R, S, from West; T, U, V, X, 
 from Kofoid ; W, from Schewiakoff. 
 
 Fritsch (46) this recalls the autospore formation characteristic 
 of the Scenedesmace^e and Phytheliaceae among the Protococcales. 
 Included in the unicellular Chlamydomonadaceae are two colourless 
 saprophytic forms — Polytoma (France, 43; Prowazek, 117) which 
 is probably derived from Chlamydomoiias, and CJilaniydohlepharis 
 which resembles Coccomonns. In his recent classification of the 
 Volvocales, Wille (150) includes in the Chlamydomonadace^ the 
 genera N ephroselmis and Glonococcus, but the former is better placed 
 among the Cryptomonads, while the latter belongs to Tetrasporaceae. 
 Of the six genera appended by Wille to the Volvocales as doubtful 
 forms, Glceomonas may be placed near Chloronionas, despite its 
 possession of numerous chloroplasts; Cylindromonas and Mesostig]ua 
 probably belong to Euglenineae, and Tetratoma to Carteriacese ; 
 Xantliodiscus and Kleiniella are still imperfectly known, though 
 Lemmermann (85) places the former in the Cryptomonadineae, 
 while France (43) regards Kleiniella as allied to Coccomonas and 
 Clilaniydohlepharis. 
 
 As pointed out by Fritsch (46), of the three attempts at coeno- 
 hium formation seen in the Volvocales, that represented by Goninm 
 has alone proved successful and has given rise to the remarkably 
 complete ascending series which culminates in Volvox. Schussnig 
 (133) has recently described in detail the life history of Goninm 
 pecforale, and has shown that in addition to the formation of daughter 
 colonies and zoogonidia, reproduction occurs by means of aplano- 
 spores and by the conjugation of isogamous zoogametes; while 
 Harper (54) has carefully studied the structure and division of the 
 Goninm colony. Pringsheim’s observation that Pandorina shows 
 heterogamy does not appear to have been repeated by recent writers 
 on the life history of this genus ; while no further observations on 
 the peculiar genus Platydorina (Fig. 4,T to V) have apparently been 
 made since its discovery by Kofoid (70) and its life history is still 
 unknown. Schewiakoff’s genera MastigosplicBra and Stephanoon (126) 
 appear to bridge the gap between Pandorina and Eudorina, though 
 their life history is unknown. In Mastigosphcera, the cells, which 
 have but one flagellum, are less closely packed in the spherical 
 coenobium than is the case in Pandorina ; while in Stephanoon 
 (Fig. 4, W) the cells are arranged on the equator of the coenobium, 
 as in Stephanosphcera, but in two alternating rows. In Eudorina the 
 cells are spaced out at the periphery of the spherical coenobium, 
 though showing a tendency to be arranged in circles, hut all the 
 cells are alike capable of reproduction, whereas in Pleodorina and 
 Volvox there is differentiation into vegetative and reproductive cells. 
 Until recently, Pleodorina with two species — P. calif ornica Shaw 
 (138), P. illinoisensis Kofoid (69) — was known only from the United 
 
Volvocales. 
 
 IQ 
 
 States, but P. califovnica has since been discovered in Ceylon 
 (Fritsch, 47), in France (Chattoiij 23), and in Java (Woloszynska, 
 154), while P. illinoisensis has been found near Heidelberg (Merton, 
 92), and the life history of this genus has been worked out in detail 
 by Chatton and by Merton. In P. illinoisensis (Fig. 4, X) the 
 coenobium consists of 32 (more rarely 16 or 64) cells, arranged 
 in five circles, the two polar circles having four cells each and the 
 other three circles eight cells each ; the cells of the anterior polar 
 quartette are vegetative only, never dividing to form new coenobia 
 and are smaller than the remaining cells. This species thus forms 
 a transition from Endorina to Pleodovimi californica, in which 
 the coenobium consists of 64 or 128 cells and is sharply 
 divided into an anterior hemisphere in which the cells are 
 purely vegetative and only one-third to one-half as large as the re- 
 productive cells of the posterior hemisphere. In Pleodorina the 
 cells have two contractile vacuoles and numerous pyrenoids, and 
 
 Volvox 
 
 Pleodorina californica 
 Pleodorina illinoisensis 
 ^ Eudorina 
 
 Stephanoon ( ? ) 
 
 Scyajnina*^ Mastigosphaera (?) 
 Pandorina 
 
 T Platydorina 
 
 Gonium — ' 
 
 Cloeomonas 
 
 Pteromonas 
 
 Phacotus 
 
 Coccomonas 
 
 i 
 
 Chlamydoblepharis 
 
 Lobomonas 
 
 Brachiomonas 
 
 Polytoma 
 
 ^Agloe 
 
 Ch. lamydomonas^ 
 
 "f Stephanosphaera 
 
 Chlorogoni’jm 
 
 T — Sphaerella 
 
 ■')unaliella 
 
 Spondylonorum 
 Chlorodendron ^ 
 
 Carteria 
 
 N 
 
 Pyramimonas^ Tetrablepharis 
 
 Chloraster 
 Polyblepharis 
 
 Chloromonadineae 
 
 Chrysomonadineae 
 
 Autotrophic Multicilia — like 
 Ancestors 
 
 Table B.— Suggested Phylogeny of the Volvocales. For details, see Text. 
 
 the chloroplast is reticulate ; in both species, oogamous sexual 
 reproduction occurs as in Endorina, any of the potentially repro- 
 ductive cells producing either a mass of antherozoids, an oosphere, 
 or a daughter-coenobium. The two species of Pleodorina form 
 perfect connecting links between Eudorina and Volvox, in which 
 last genus the vast majority of the cells in the large coenobium are 
 vegetative and there is still more pronounced differentiation between 
 
20 
 
 Flagellata and Primitive Algce. 
 
 the vegetative and the reproductive cells and more marked oogamy, 
 the oogonial cells being differentiated at an early stage in the form- 
 ation of the coenobium and having no flagella. Van Tieghen’s genus 
 Scyaniina is an imperfectly known colourless form, in which the 
 numerous cells are placed at different depths in the spherical 
 coenobium, instead of being confined to the periphery as in Endorina; 
 it is quite uncertain whether it represents a saprophytic offshoot 
 from a Eudorina-Wko. type, or a form derived from Polytoma by 
 coenobial development, or indeed whether it is rightly placed in the 
 Volvocales at all. 
 
 The inter-relationships of the Volvocales, as here suggested, 
 are indicated on the accompanying Table B. 
 
 VI. — The Chrysomonads. 
 
 Since the publication of Senn’s compilation in 1900, much work 
 has been done on the Flagellate forms included by him in the 
 Chrysomonadineae and Cryptomonadineae. From the extensive re- 
 cent literature of these forms, to which Pascher has been the largest 
 contributor, it will suffice to select for mention certain results which 
 are of special interest in connexion with the phylogeny of the Algae. 
 Various new genera have been added to those enumerated by Senn, 
 and some modifications of the earlier classification have been 
 suggested. Senn divides the Chrysomonadineae into three families 
 characterised respectively by the possession of a single flagellum 
 (Chromulinaceae), two equal flagella (Hymenomondaceae), and two 
 unequal flagella (Ochromonadaceae). Scherffel (125) has shown 
 that Monas, Oikoniojias, and various other genera placed by Senn in 
 the Protomastigineae are better regarded as colourless forms derived 
 Chrysomonads; for instance, they show precise agreement with 
 normal coloured Chrysomonads in producing leucosin, in the mode 
 of encystment, and in various cytological details. In describing a 
 new species of Gymnodinmm, a genus belonging to the simpler 
 Peridiniales which have been regarded as derived from the Chryso- 
 monadineae (see below), Ohno (94) criticises the systematic value of 
 the flagellum number in the classification of the Flagellata. This 
 new species differs from all other Peridiniales in having two longi- 
 tudinal flagella instead of one, in addition to the usual transverse 
 flagellum, but otherwise must be placed in the genus Gyninodinium. 
 The same objection has been raised with regard to the lower Green 
 Algae,^ but Senn’s classification is accepted by Pascher and other 
 recent writers on the Chrysomonads, since (as in the case of the 
 Green Algae) the groups are distinguished by characters other than 
 the number of flagella. In Pascher’s suggested classification (101), 
 the Cryptomonads are merged in the Chrysomonadineae, which are 
 divided into four orders. The first three of these (Chromulinales, 
 Isochrysidales, Ochromonadales) coincide with Senn’s three families 
 of Chrysomonadineae, while the fourth ( Phaeochrysidales) is charac- 
 terised by the possession of laterally inserted flagella — in the other 
 three orders the flagella are terminal —and includes the Crypto- 
 monadineae of Senn. 
 
 2,See Review of Wille’s classification of Green Algae, by R.P.G., New 
 Phytologist, vol. IX., 1910, p. 78. 
 
The Chrysomonads, 
 
 2 1 
 
 The Chrysomonads are characterised by a peculiar endogenous 
 method of cyst formation. Before a definite cyst appears, there is 
 visible within the protoplast a membrane covered by an amoeboid 
 protoplasmic layer (Fig. 5, 11-14), which produces sculpturing on the 
 outer surface of the cyst membrane, hut later this protoplasm 
 retreats within the membrane through a pore which has been left, 
 this pore being afterwards closed by a plug which in some cases 
 consists of cellulose ; the membrane usually contains silica. A 
 similar method of cyst formation occurs in certain colourless 
 heterotrophic genera which have hitherto been placed in the 
 Protomastigineas, and on this ground, as well as on account of 
 other cytological resemblances, it is suggested that these forms 
 should be transferred to the Chrysomonads. These forms, which 
 may be regarded as colourless derivatives from normal autotrophic 
 Chrysomonads — corresponding with the colourless forms (Polytoma, 
 etc.) included in the Volvocales — belong to the genera Monas, 
 Oikomonas, Dendromonas, Antophysa, Cephalothamnion, etc. It 
 would appear that further investigations will lead to a consider- 
 able number of genera being transferred from the Protomastigineae 
 to the Chrysomonads, and doubtless to other groups of pigmented 
 Flagellata, if we accept the view that where colourless and 
 coloured Flagellates show close agreement in every character 
 save the presence or absence of assimilatory pigments, the 
 colourless forms are to be regarded as having arisen from the 
 coloured as an adaptation to a heteroti’ophic mode of nutrition. 
 
 The recent work of Pascher, Scherffel, Senn, and others has 
 shown that the Chrysomonadine^e (in the wider sense, as defined 
 by Pascher) form a remarkably diversified group, in each order of 
 which various parallel developments may he traced, starting from 
 relatively simple free-living and usually small forms. The chief of 
 these parallel developments are the formation of motile colonies 
 analogous with those of the higher Volvocales, and of variously con- 
 structed non-motile colonies corresponding with those of the 
 Tetrasporaceas and other families of Protococcales characterised 
 by aggregation of the cells into mucilaginous masses ; the occurrence 
 of amoeboid forms and of amoeboid phases, the latter perhaps to be 
 regarded as reversions to an ancestral condition ; the lobing, division 
 and further elaboration of the primitively indefinite and reticulate 
 or basin-shaped chromatophore ; the coordination of the contractile 
 vacuoles to form a pulsating vacuole system similar to that seen in 
 the Chloromonadine^e and Eugleninese ; the substitution of solid 
 carbohydrate assimilates (paramylum and starch) for oil and 
 leucosin; the elaboration of the outer protoplasmic layer into a firm 
 periplast and finally into a definite membrane (in some cases con- 
 sisting of cellulose) which may form either a close-fitting or an 
 outstanding and cup-like perisarc ; the outgrowth of tentacles from 
 the periplast ; and the development of sculpturings and of various 
 excrescences (ridges, spines, etc.) on the cell-wall. 
 
 The Chromulinales include the simplest forms of the Chryso- 
 monadineje. In the lowest family, Chrysapsidaceae, the cells are 
 free-living and are amoeboid ; in Chvysapsis the chromatophore is an 
 indefinite reticulate peripheral sheet, while in CluysaiiKjeha and 
 Nannoclirysis it is basin-shaped, though in some species of Chrys- 
 
2 2 Flagella ta and Primitive Algce. 
 
 amceba it becomes deeply bilobed and even divided into two (Fig.5, 1,2). 
 In Chrysapsis, division often occurs within a gelatinous investment, 
 while in NannocJirysis the formation of a palmella-stage is more 
 pronounced and several divisions occur before the products of 
 division become free by dissolution of the jelly. These simple forms 
 show marked resemblance to some of the simpler Protomastiginese ; 
 Chrysaniceha is very similar to Mastigamceha and Oikomonas, apart 
 from the absence of a chromatophore in the latter genera. 
 
 The Chromulinacese, forming the largest family of Chromuli- 
 nales, include solitary and colonial forms, the former showing a 
 elaboration of the protoplast as compared with the Chrysapsida- 
 ceae ; there is usually a single basin-shaped chromatophore, but 
 sometimes two or even more may be present. Among the solitary 
 forms, Chvysococcus (Fig. 5, 15, 18) has a thick shell or perisarc 
 closely investing the periplast, but with a small anterior opening 
 for the flagellum, the periplast of some species is ornamented with 
 wart-like out-growths, and there is either a basin-shaped chromato- 
 phore or two lateral curved plate-like chromatophores, or several 
 discoid chromatophores (Pascher, 99). A further elaboration is 
 seen in the curious epiphytic genera Chrysopyxis and Stylococcus, in 
 which the body is amoeboid and lies loosely within a goblet-like shell 
 or perisarc which projects freely beyond it, and is produced at the 
 base into a hapteron ; longitudinal division occurs within the shell, 
 and one of the daughter-cells escapes, produces a perisarc with an 
 attaching process, and settles down ; the cell contains cellulose, 
 and the “ flagellum ” is in reality a “ rhizopodium/’ or branched 
 filamentous pseudopodium, at any rate in Chryopyxis {Fig. 5, 26-30), 
 which may be regarded as practically a Chrysamoeba that has 
 become epiphytic and produced a shell ; in Stylococcus (Fig. 5, 
 23-25), the “ flagellum ” is unbranched, but differs from the normal 
 type of flagellum in being motionless and is doubtless pseudopodial. 
 
 The colonial genera of Chromulinaceae show an advance upon 
 the Chrysapsidacese, in that the palmella stage is more enduring, 
 and in the genus Hydrurus becomes dominant. In Chromulina 
 Hokeana, division occurs in the motile state, and the products of 
 two or three successive divisions remain coherent to form a four- or 
 eight-celled motile colony, comparable with the coenobia of Goniuni 
 and Pandorina, and thus representing the “ Volvocine tendency ” 
 which has appeared independently in several distinct groups of 
 Chrysomonads. In most species of Chromulina (Fig. 5, 9-14). 
 however, division occurs in a resting palmella state (after the cells 
 have lost their flagellum), giving rise to an indefinite mucilaginous 
 mass ; the free flagellate cells are amoeboid and resemble Chrysa- 
 mceba. A far more enduring and definite palmella state occurs in 
 Hydrurus (Fig. 5, 37-41); the motile cells (‘-zoogonidia”) are of 
 tetrahedral form, with the flagellum at the broader anterior end 
 and on coming to rest lose the flagellum, become attached 
 assume an ellipsoid form, secrete a mucilaginous stalk, and by 
 repeated division give rise to an elaborately and regularly branched 
 colony of considerable size. In this colony the cells are more 
 crowded in the smaller branches than in the main axis and the 
 larger branches ; the whole structure behaves like a multicellular 
 plant, growth in length depends on single apical cells, and the zoo- 
 gonidia are produced from the branches, two or four arising by 
 division of a parent-cell. 
 
The Chrysomonads, 23 
 
 Fig. 5. Chromulinales. — 1 and 2, Chrysamceba radians Klebs : 1, a 
 
 normal free swimming individual ; 2, an amoeboid form. 3 to 9, Chromnlina 
 Rosanoffii (Woronin) Biitschli : 3, motile cell or zoogonidium ; 4 to 7, division of 
 a motionless encysted cell floating on the surface of the water ; 8 and 9, for- 
 mation of palmella stage. 10, Chromnlina ovalis Klebs, motile cell. 11 to 14. 
 Chromnlina nehnlosa Cienk.. showing development of cyst : in 11 and 12, a portion * 
 
24 
 
 Flagellata and Primitive Alg<t. 
 
 of the protoplasm is extruded from a pore, this amoeboid mass being Used up 
 in the formation of the cyst membrane; 13 and 14 are different views of the 
 fully formed cyst. 15 to 18, Chrysococcus ritfescens Klebs : 15, a motile cell, in 
 optical section, showing projection of the flagellum through a pore in the thick 
 perisarc ; 16, division of the protoplast; 17^ escape of a daughter-cell; 
 18, free daughter-cell, before formation of perisarc. 19, Microglena punctifera 
 Ehrb., showing the vacuole system. 20, Mallomonas litomesa Stokes, with 
 flinty processes at anterior and posterior ends of the cell, 21, Mallomonas 
 acaroides Ehrb., with similar processes nearly covering the cell. 22, 
 Mallomonas pulcJieyrima Stokes, showing in part the reticulate sculpture 
 of the perisarc. 23 to 25, Stylococcus aureus Chodat : two stages of division 
 in 24 and 25. 26 to 30, Chrysopyxis bipes Stein : in 26 the flagellum is forked; 
 
 27 shows longitudinal division into two daughter-cells ; 28 and 29, a daughter- 
 cell with elongating posterior process for attachment— in 30 this process has 
 wound around a Zygncma filament, part of which is seen in transverse section 
 at the base of the sessile flask-like perisarc. 31, Lagynion Scherffeli Pascher. 
 32, Heterolagynion Oedogouii Pascher : to the left of the stout motionless flagellum 
 is a short blunt pseudopodium (pseud.) ; within the stout perisarc the protoplasm 
 contains a nucleus (nu.), a food vacuole (f.v.), two contractile vacuoles (c.v.), 
 and two leucosin masses (leuc.) 33, Pedinella hexacostata Wys., with four stiff 
 bristles at the base of the flagellum ; on the right is an amoeboid pseudopodium 
 containing a food vacuole. 34, Cyrtophora pedicellata Pascher, showing the 
 central flagellum, the stout nodulose tentacles, and several pseudopodial pro- 
 cesses at the anterior end of the protoplast. 35, Palatinella cyrtophora Laut., 
 with short flagellum in the centre of the ring of tentacles. 36, Chrysospharella 
 longispina Laut., a motile coenobium of Chromulina-Wkc cells, each with two long 
 flinty processes exserted from cup-like outgrowths of the periplast. 37 to 41, 
 Hydrurus fadidus (Vauch.) Kirchner : 37, a motile cell or zoogonidium; 38, 
 motionless cell, which becomes attached by a gelatinous stalk (39) and by 
 division (39) gives rise to the branching colony, a portion of which is shown 
 in 41. 
 
 1, 2, 10, 15 to 19, 21, 37 to 40, from Klebs; 3 to 9, from Woronin ; 11 to 
 14, from Cienkowsky ; 20, 22, from Stokes ; 23 to 25, from Chodat ; 26 to 30, 
 from Stein; 31, 32, 34, from Pascher; 33, from Wysotzki ; ^35, 36, from 
 Lauterborn ; 41, from Berthold. 
 
 Hydrurus and other palmelloid Chrysomonads have been 
 regarded by some writers as belonging to the Phaeophyacese, on 
 account of the dominance of the palmella stage in the life history, 
 but apart from the fact that various degrees of elaboration of this 
 stage have been observed in undoubted Flagellates, the terminal 
 insertion of the flagella in the lower Chrysomonads, as compared 
 with the characteristic lateral flagella of the Brown Algse, seems to 
 form an insuperable obstacle to the derivation of the Phaeophyce^e 
 from these Chrysomonads. Despite the dominance and elaboration 
 of its palmella stage, Hydrurus can hardly be said to have crossed 
 the “border-line” between Flagellates and Algae; it is simply a 
 Flagellate, allied closely to the lower Chrysomonads, and represents 
 the culmination of a line of palmelloid forms arising from types like 
 Chrysapsis and Nannochrysis. The “ Volvocine tendency ” shown 
 in Chromulina Hokeaua is carried further in Chrysostephanosphccra, 
 recently discovered by Scherffel ; here the coenobium consists of 
 sixteen cells arranged as in Stephanosphcera on the equator of a 
 globular gelatinous mass, but later a palmelloid state is produced 
 in which each cell has its own mucilaginous envelope. 
 
 Further elaboration in the external and internal characters of 
 the cell is seen in the small family of Mallomonadaceae, consisting 
 of the two free-living genera Malloiiionns and Microglena and the 
 colonial genus Chry so splicer dla. In Mallomonas (Fig. 5, 20-22) the 
 
The Chrysomonads. 25 
 
 ovoid or elongated cell has a close-fitting shell composed of tesselated 
 polygonal plates, and either each plate, or only those at the two 
 ends of the body, may bear fine silicified outgrowths; there are two 
 chromatophores, and the hinder end of the cell contains numerous 
 contractile vacuoles, while at the anterior end there is a large non- 
 contractile vacuole ; the cysts are also covered with a silicified shell. 
 In Microglena (Fig. 5, 19) the vacuole system is further elaborated, 
 all the vacuoles being anterior, the smaller contractile vacuoles 
 surrounding a large non-contractile vacuole ; there is frequently a 
 single basin-like chromatophore ; the sliell is thin and bears only 
 scattered granular outgrowths. In Clirysosphcerella (Fig. 5, 36) the 
 cells are united by their hinder ends in a spherical jelly, forming a 
 motile Pandorina-Vike coenobium ; each cell bears on its free outer 
 (anterior) end two small cup-like outgrowths from the shell (which 
 has the same structure as in Mallomonas) and from each of these 
 cups there springs a long flinty spicule ; the internal structure of 
 the cells resembles that o\ Microglena^ there are two chromatophores, 
 each with a stigma. 
 
 Pascher (102) has founded a fourth family of Chromulinales, 
 the Cyrtophoraceae, upon three very remarkable epiphytic genera 
 which have probably arisen from a type like Chrysopyxis. These 
 genera — Pedinella, Palatinella, Cyrtophora (Fig. 5, 33-35) — are 
 either sessile or stalked, the body is flattened anteriorly and bears 
 a central flagellum surrounded by from six to twenty pseudopodia ; 
 there is a single basin-shaped chromatophore, but this is more or 
 less deeply lobed in front. Pascher (109) has recently described a 
 genus (Lagynion) which forms a transition between Chrysopyxis 
 and the Crytophoraceae ; in Lagynion (Fig. 5, 31) the cell is fixed by 
 a broad base, and within the collar- like projecting portion of the 
 shell the protoplast protrudes short amoeboid pseudopodia around 
 the base of the long motionless flagellum or “ rhizopodium.” The 
 same writer describes a colourless genus, Heterolagynion {F\g. 5,32,) 
 evidently derived from Lagynion, and points out that the Cyrto- 
 phoraceae show a remarkable parallelism with the Pantostoma- 
 tinean genera Pteridomonas and Actinomonas. 
 
 In the Isochrysidales the cells are either free-living or united to 
 form colonies of the Volvocine type. Of the nine genera placed here 
 (as Hymenomonadaceae) by Senn, the unicellular genus Wysotzkia 
 sliould be transferred to the Phaeochrysidales (Cryptomonads), and 
 the palmelloid genera Phceocystis (Ostenfeld, 96), and Ncegeliella 
 (Correns, 27) to the Phaeocapsaceae ; in these three genera the 
 two flagella are inserted laterally, and while Wysotzkia is clearly 
 related to the simpler Cryptomonads, especially to the two recently 
 discovered genera Protochrysis and Cryptochrysis, it seems equally 
 obvious that the affinities of Phceocystis and Ncegeliella are with the 
 lower Phseophyceae, hence they should be removed from the Brown 
 Flagellata altogether. In the simplest Isochrysid genus, Hymeno- 
 monas (Fig. 6, 7), the cell has a firm thick periplast, though the 
 anterior portion of the protoplast is naked and capable of putting 
 forth pseudopodia. In this order, evolution appears to have taken 
 place in two directions, one leading to epiphytic forms recalling 
 Chrysopyxis and its allies among the Chromulinales, the other to 
 motile colonies. Of the epiphytic forms, Stylochrysalis (Fig. 6, 3), 
 
^6 
 
 Flagellata and Primitive Algce. 
 
 is attached to its substratum (usually an Eudorina colony), by a 
 long stalk dilated at the base, and has a thin periplast ; while 
 Derepyxis (Fig. 6, 2) resembles in having an outstanding 
 
 perisarc with a projecting collar. Of the colonial forms, Syncrypta 
 and Synnva have globose motile coenobia, consisting of 16 to 64 
 
 Fig. 6. ISOCHRYSIDALES (1 tO 6) and OCHROMONADALES (7 tO 16). — 1, 
 Hymenonionas roseola Stein. 2, Derepyxis dispar Stokes. 3, Stylochrysalis parasitica 
 Stein (in 4, transverse division is shown). 5, Synnra Uvella Erhb. 6, Syncrypta 
 Volvox Erhb. 7, Ochromonas crenata Klebs. 8 to 10, Ochromonas mutahilis Klebs, 
 showing migration of food vacuoles within the protoplasm and amoeboid changes 
 of form of the cell. 11, 12, Cyclonexis annularis Stokes : in 11 the coenobium is 
 seen from the surface, in 12 from the side. 13 to 16, Dinobryon Sertularia Ehrb. : 
 in 14 to 16, stages in division and perisarc formation. 
 
 1, from Klebs; 2, 11, 12, from Stokes; 3 to 6, from Stein ; 7 to 10, 14 to 
 16, from Klebs; 13, from Senn. 
 
 biflagellate individuals closely aggregated in a radial manner, their 
 pointed hinder ends directed towards the centre of the coenobium ; 
 in Syncrypta (Fig. 6, 6) the cells have a thin periplast and the 
 
The Cryptomonads and their Relationships. 27 
 
 colony is invested in mucilage through which the flagella protrude, 
 in Synura (Fig. 6, 5) there is no mucilaginous covering and 
 each cell of the colony has a firm periplast beset with spines or 
 warty outgrowths — in 5. Klebsiana each cell bears .two flinty 
 spicules, as in Chry so splicer ella. Pascher (110) has observed that 
 in Synura uvella the contents of a cell may escape as an amoeba 
 instead of a flagellate swarmer, and that the latter may also 
 become amoeboid after liberation, and that from both flagellate 
 and amoeboid forms palmella-states may arise by division in a 
 mucilaginous motionless condition (Conrad, 26). 
 
 The Ochromonadales, though a smaller order than the Chro- 
 mulinales and Isochrysidales, shows parallel developments of the 
 same kind. Here again we begin with a unicellular and potentially 
 amoeboid type, Ochromonas (Fig. 6, 7-10), which, except in having 
 two unequal flagella, closely resembles Chrysamceba among the 
 Chromulinales ; most of the species are free-swimming, but 0. 
 tenera becomes fixed by its hinder end ; the thin periplast is 
 capable of secreting mucilage, and in 0. socia division occurs in the 
 motile phase and gives rise to small, generally four-celled, motile 
 coenobia ; usually, division occurs in a resting state, and in O. 
 botrys a large mass of cells enveloped in mucilage may be formed 
 in this way. In Cijclonexis (Fig. 6, //, 12), the individual cells are 
 like those of Ochromonas, but they remain in lateral contact in 
 such a manner as to form a radiating ring-like coenobium, con- 
 sisting usually of 16 cells. In Uroglena a curious type of coenobium 
 is formed as the result of repeated division of the stalked cells and 
 the formation of a spherical mucilage mass in which the cells lie 
 near the periphery while the branching stalks radiate from the 
 centre. In Dinobryon (Fig. 6, 13-16) the cell is spindle-shaped and 
 is invested loosely by a vase-like shell widely open above ; when 
 division occurs, the daughter cells may either escape or (in most 
 species) become attached to the mouth of the shell and produce a 
 shell of their own ; by repetition of this process, a branching colony 
 is built up; the shell in some cases gives cellulose reactions. The 
 genus Dinobryon has been monographed by Brunnthaler (16) and 
 by Lemmermann (79). 
 
 VII, — The Cryptomonads and their Relationships. 
 
 I T would appear that the three orders of Chrysomonadineae 
 dealt with thus far (Chromulinales, Isochrysidales, Ochromo- 
 nadales) have not given rise to anything higher than a Flagellate, 
 though they show various attempts at the formation of colonies 
 — in all three orders we find gradual elaboration of motile 
 “ Volvocine” coenobia, and also the working out of a palmelloid or 
 “ Tetrasporine ” tendency towards the formation and dominance 
 of a non-motile multicellular vegetative condition. It may be 
 noted that “ Volvocine ” coenobia occur also among the Proto- 
 mastigine^e {Protospongia, Sphcerceca, etc.), in addition to the 
 dendroid colonies of the Dinobryon type {Codonocladium, Salpingocca, 
 etc.) derived from solitary “ choanflagellate ” forms {i.e., forms 
 with outstanding collar-bearing perisarc). Whether the remark- 
 able resemblances between the “ mastigamoeboid,” the “ Volvo- 
 
28 Flagellata a 7 td Primitive Algce. 
 
 cine,” and the solitary and dendroid “ choanoflagellate ” types 
 met with in the colourless Pantostomatineae and Protomastigineae 
 on one hand and the Chrysomonadine^e on the other are to be 
 interpreted as examples of parallel developments, or whether, as 
 suggested by Pascher and Scherffel, they indicate derivation of 
 part at any rate of the colourless P'lagellate families from Chryso- 
 monads, the trend of recent work on tlie Brown Flagellata is 
 decidedly against the view that the Chrysomonads comprised in 
 families Chromulinales, Isochrysidales, and Ochromonadales have 
 given rise to the Brown Algae. 
 
 The case appears to be quite different with the fourth Chryso- 
 monad order, the Phaeochrysidales or Cryptomonads, which are 
 distinguished hy the lateral insertion of the two flagella. The 
 simplest forms are Pascher’s new genera Cryptochrysis and Proto- 
 chrysis (103) ; Wysotzkia (hitherto placed in the Isochrysidales) ; 
 and Nepliroselmis (Senn, 136), which Wille (150) includes in the 
 Volvocaceae. Senn (135) defines the Cryptomonads as having an 
 ovoid and flattened body, with two equal flagella arising just behind 
 the anterior end from a groove which is continued into a gullet-like 
 cavity, and having one or two contractile vacuoles which are not 
 coordinated into a pulsating system. According to Senn they are 
 also further differentiated from the Chrysomonads by producing 
 starch, or, at any rate, a refractive solid carbohydrate. The 
 researches of Pascher and others have shown, however, that the 
 Cryptomonads, though a highly specialised group, cannot be set 
 apart from the Chrysomonads, as a separate group of the Flagellata, 
 and that they have arisen from the Chrysomonads by further internal 
 differention of the protoplast, accompanied by a shifting of the 
 flagella from a terminal to a lateral position. In Wysotzkia (Fig. 
 7, 3, 4), the posterior end of the protoplast, behind the two chromato- 
 phores, is naked and capable of amoeboid movement. In Crypto- 
 chrysis (Fig. 7, 2), the lateral insertion of the flagella is more 
 marked than in Wysotzkia, the flagella arising from a deep longitu- 
 dinal groove which is about half the length of the body and is 
 covered with minute granules; nutrition is purely holophytic and 
 the assimilate consists of disc-like grains giving a reddish violet 
 colour with iodine ; division takes place in the motile state, and is 
 longitudinal. 
 
 Cryptochrysis appears to be the most primitive Cryptomonad 
 at present known ; Wysotzkia, though simpler in some respects, 
 undergoes transverse division, and is adapted for partial or 
 facultative holozoic nutrition. Nepliroselmis and Protochrysis 
 differ from these genera, and indeed from the remaining Crypto- 
 monads, in that the groove is transverse and occupies the middle 
 of the protoplast, so that the flagella arise from the middle of the 
 concave side of the body ; in Nephroselmis there is a single chroma- 
 tophore which follows the outline of the body and is interrupted 
 only at the point of emergence of the flagella, and division occurs 
 in the motile condition, whereas in Protochrysis (Fig. 7, /), there 
 are two chromatophores, and division occurs after the cells have 
 become rounded off and invested in mucilage, a four- or eight- 
 celled colony being formed by repeated division in this palmella- 
 state. In Cryptomonas (Fig. 7, 5 — 7), the groove found in the 
 
The Cryptomonads and their Relationships. 29 
 
 genera just mentioned is replaced by a canal which leads into the 
 interior of the protoplast ; in some species this canal is quite short, 
 in others it extends for about half the length of the body. In most 
 species of Ciypionionas the assimilate is like that found in Crypto- 
 
 Fig. 7. Cryptomonads (1 to 9) and Ph^ocapsace^ (10 to 19) : — 
 1, Protochrysis pJusophyceanim Pascher. 2, Cryptochrysis commutata Pascher. 
 3, 4, Wysotzkia hiciliLita (Wys.) Lemmerm, : 3, ordinary form ; 4, metabolic 
 (amoeboid) form, showing protrusion of pseudopodia anteriorly and posteriorly. 
 5 to 7, Cryptomonas erosa Ebrb. : 5, ordinary motile cell ; 6, two encysted cells 
 with gelatinous envelopes; 7, ruptured cyst membrane. 8, Chilomonas 
 Parcmcecium Ebrb. : the flagella arise on the ventral side of the “ gullet ” 
 (which shows several circles of granular markings in its lower half), from a 
 small body which is connected with the nucleus by means of a long fibril. 
 9, Cyathomonas truncata (From.) Fresen. : structure essentially as in Chilomonas ; 
 there are numerous food vacuoles at the base of the cell, the single contractile 
 vacuole is seen near the opening of the “ gullet.” 10 to 12, Phaoplax marina 
 (Reinisch) Pascher: 10, motile cell ; 11 and 12, young colonies (beginning of 
 palmella stage, which when fully developed resembles that seen in Chromnlina 
 Rosanoffii, Fig. 5, P). 13 to 15, PhcBocystis Poucheti Lagerh. : 13, gelations colony 
 
 (palmella state) ; 14, a portion of same, more highly magnified) ; 15, a motile 
 cell (zoogonidium). 16 to 19, Nagcliella fla^ellifera Correns : 11 and 12, one-celled 
 and three-celled stages in development of colony, showing the perisarc and 
 bristles ; 18, a single cell, showing the bell-shaped chroniatophores ; 19 a 
 motile cell (zoogonidium). 
 
 1, 2, from Pascher; 3, 4, from Wysotzki ; 5 to 7, from Senn ; 8, 9, from 
 Ulehla (with some details inserted from Hartmann and Chagos) ; 10 to 12, 
 from Reinisch ; 13, 14, from Lagerheim ; 15, from Pouchet ; 16 to 19, from 
 Correns. 
 
30 Flagellata and Primitive Algce. 
 
 clirysis, but in C. ovata starch is produced ; longitudinal division 
 may occur in either the motile or the encysted condition, and the 
 cyst membrane gives the reactions of the cellulose. Chroomonas 
 and Cyanomonas resemble Cryptonionas, but the chromatophores 
 are blue-green, while Rhodomonas is allied to these forms but has a 
 red chromatophore. Chilomonas (Fig. 7, 8) also resembles Crypto- 
 monns in structure, but is saprophytic, though it produces starch ; 
 Botryowonas (Schmidle, 131) is another saprophytic starch-pro- 
 ducing form, in which the cells become aggregated to build up a 
 branched gelatinous colony, and the periplast gives cellulose 
 reactions. Cythomonas (Ulehla, 143) and Oxyrrhis (Senn, 136), 
 though placed by Senn in the Protomastigineae, are apparently 
 related closely to Cryptomonas through Chilomonas, and may be 
 regarded as colourless forms derived from a Cryptomonas-Wko. type ; 
 in Cyathomonas (Fig. 7, 9) nutrition is mainly saprophytic, but solid 
 food can also be ingested at the anterior end of the body, while in 
 Oxyrrhis nutrition is mainly holozoic and this genus differs from 
 its allies in undergoing transverse division. 
 
 The Cryptomonads have probably arisen from simple Chryso- 
 monads, with two flagella either of unequal length or with different 
 orientation (one directed forwards and the other backwards in 
 swumming). Such a form as Ochromonas, for instance, may well 
 have given rise to the Chloromonadinese on one hand and to the 
 Cryptomonads on the other, for these two groups show somewhat 
 striking parallelisms, such as the organisation of the vacuole 
 system into small actively contractile vacuoles which open into a 
 large anterior non-contractile vacuole or into a groove or canal. 
 The Chloromonads have probably given rise on one hand to the 
 highly differentiated Eugleninese which have no Algal affinities, and 
 on the other to the Algal group “ Confervales ” (Heterokontae). 
 Similarly the simpler Cryptomonads — e.g., Cryptochrysis and 
 Protochrysis — appear to have given rise on one hand to highly 
 organised Flagellates like Cryptomonas, Chilomonas, Cyathomonas, 
 and Oxyrrhis — corresponding to the Euglenineae in the green 
 series — and on the other to the Phaeocapsaceae, which form the 
 starting-point of the Brown Algae. 
 
 The Phaeocapsaceae, corresponding roughly with the 
 Tetrasporaceae and Palmellaceae in the green series, are apparently 
 a somewhat heterogenous group, marked by the dominance of the 
 non-motile phase. One of the simplest genera is PhcBocystis 
 (Fig. 7, 13-15) in which the cells have from one to four plate-like 
 chromatophores and are aggregated to form a rounded gelatinous 
 colony, the motionless cells being rounded, while the motile cells 
 (“ zoogonidia ”) are biflagellate and have the same structure as 
 Wysotzkia (Lagerheim, 73; Ostenfeld, 96; Scherffel, 122). In a 
 similar form described by Reinisch (120) as Phcsococcns marinus 
 (Fig. 7, 10-12) but regarded by Pascher (104) as the type of a new 
 ff^enus, Phceoplax, the motile cells correspond closely to Cryptochrysis. 
 PhcBococcus dementi is a gelatinous form adapted to subaerial life, 
 the cells having firm envelopes, and the motile cells show typical 
 Cryptomonad structure ; whether P. paludosa described by West 
 (146) belongs to this genus, or indeed to the Phaeocapsace^, is 
 somewhat doubtful, since in his figures the motile cells resemble 
 those of the Isochrysidal Chrysomonads and not the Cryptomonads, 
 
The Cryptomonads and their Relationships. 31 
 
 The position of Phceosphcera West is also doubtful, as the motile 
 cells have apparently not yet been observed ; the same is the case 
 with Stichoglcea and Gleothamnion, which would be included in the 
 Phaeocapsacese if their motile cells were found to show Cryptomonad 
 characters. N<^geliella is epiphytic and forms multicellular discs, 
 the individual cells producing a perisarc prolonged into a bristle ; 
 the motile cells have a single brown chromatophore and two 
 laterally inserted flagella. The genus PhcBothamnion appears to 
 represent the highest form of the Phasocapsaceae, w'hile Pleurocladia 
 leads directly to the Ectocarpaceae and is placed in that group by 
 Kjellman and Svedelius (66). A useful bibliography of the genus 
 Phceothaiunion is given by M’Keever (91), who recently discovered 
 P. confervicolum (the only species known) in Scotland — it was 
 previously recorded only from Sweden, Germany and Italy. There 
 appears to be some doubt as to the insertion of the flagella and the 
 nature of the motile cells ; according to Lagerheim the latter are 
 zoogonidia with terminal flagella and no eye-spot, while Borzi 
 described the conjugation of isogamous gametes with lateral 
 flagella and a red stigma. Oltmanns (95) places PhcBothamnion, 
 with the other genera here regarded as forming the family 
 Phaeocapsacese, among the Chrysomonadinea3. This genus is, 
 however, apparently related very closely to Pleurocladia, which 
 has the typical gonidangia and gametangia of the Ectocarpaceae. 
 Bohlin’s genus Phceodactylon (9) cannot be included in the Phaeo- 
 capsaceae, but is probably a Chrysomonad in which adaptation to 
 plankton conditions has resulted in loss of the flagella ; its curious 
 three-armed cell recalls the tetrahedal motile cells of Hydrurus. 
 
 The greatest difficulty in the way of deriving the Phaeophyceae 
 from the Brown Flagellates has been the characteristic lateral 
 insertion of the flagella in the motile cells of the Brown Algae — 
 excepting in the Dictyotaceae, which are somewhat isolated 
 among the Phaeophyceaae. This difficulty has, however, been over- 
 come by the discovery of Protochrysis, in which the furrow from 
 which the flagella arise, instead of being longitudinal and subapical 
 as in other Cryptomonads, is transverse, so that the flagella arise 
 from the middle of the body, one flagellum being directed forwards 
 and the other backwards. Protoclnysis appears to stand very near 
 the ancestral type which gave rise to the lower PhseophycesB 
 or to the series of transitional forms (Phaeocapsaceae) leading 
 through Phaeothcunnion and Pleurocladia to the Ectocarpaceae. 
 
 The work of Pascher and Scherffel supports Klebs’ view that 
 the Cryptomonads have arisen from the (3hrysomonads and have 
 no direct relationships with any other Flagellate group excepting 
 possibly the Dinoflagellata (Peridiniales). Pascher, as we have 
 already seen, merges the Cryptomonads in the order Chrysomonad- 
 ineae, and has shown that the organisation of a pulsating vacuole 
 system, previously regarded as found only in the Chloromonads 
 and the Euglenineae, occurs not only in the Cryptomonads but also 
 among the Chrysomonad groups. Another distinction made by 
 previous writers between the Cryptomonads and Chrysomonads has 
 broken down, namely, that relating to the nature of the assimilation 
 products. According to Senn, the Chrysomonads produce oil and 
 leucosin, and nutrition may be holozoic or saprophytic or holophytic, 
 while in the Cryptomonads starch is produced and nutrition is 
 
32 
 
 Flagellata and Primitive A Igce. 
 
 never holozoic. Pascher has shown, however, that although starch 
 is formed in certain Cryptomonads {Cryptomonas erosa, 
 Chroomonas haltica, Chrysidella^ Chilomoiias), this is not the case 
 in other forms which have been investigated {Protochrysis, 
 Cryptoclirysis, Chroomonas N ordstedtii) nor in the Phaeocapascae, 
 where the assiniilate is either leucosin or oil. All that can be said 
 on this head is that solid assimilation products are relatively rare 
 in the Chrysomonads and relatively common in the Cryptomonads. 
 Again, the beginnings of the characteristic furrow of the 
 Cryptomonads are seen in the Ochromonadales, and even in the 
 Chromulinales, where the anterior end of the body shows a pit in 
 which the flagellum is inserted. 
 
The Peridiniales and their Relationships. 
 
 33 
 
 F rom simple Cryptomonads — like Pyotochrysls, Cryptochrysis, 
 or Wysotzkia — various diverging lines may be traced. One of 
 these leads to the endozoic “ Zooxanthella ” forms ; some at any 
 rate of the “ Zooxanthellae ” belong to the Cryptomonads and are 
 placed by Pascher in a new genus, Chrysidella. Two other lines, 
 marked by the fixation of the blue-green and the red chromatophores 
 found sporadically in the simpler Cryptomonads, lead respectively 
 to the blue-green genera Chroomonas and Cyanomonas and to the 
 red genus Rhodomonas. Another line leads to Cryptomonas and 
 NepJiroselmiSf with firm periplast, and from these have been derived 
 the colourless forms Chilomonas, Cyathomotias, and Oxyrrhis. The 
 fifth line has probably led to the Dinoflagellata (Peridiniales) on 
 one hand, and through simple palmelloid types to the Phseocapsaceae 
 on the other. In the Phaeocapsacese, beginning with simple 
 gelatinous forms like Phceoplax, PJiceocystis^ and PJic^ococcus, we 
 have a series of transitional types leading to the definitely filamentous 
 Phceothamnion and so to the Ectocarpales. 
 
 The inter-relationships of the Brown Flagellate and Algal 
 groups as here suggested are indicated on the accompanying 
 scheme (Table C). 
 
 VIII. — The Peridiniales (Dinoflagellata) and their 
 Relationships. 
 
 The Peridiniales, mainly marine but also found in fresh waters, 
 and often forming a considerable part of the microplankton, are 
 always unicellular and usually isolated, though sometimes cohering 
 in chain-like colonies and in one family (Phytodiniaceae) forming 
 palmelloid aggregations by repeated division within gelatinous 
 envelopes. There are typically two dissimilar flagella, usually lodged 
 in grooves — one longitudinal and the other transverse — and in most 
 cases the protoplasm is clad by a cellulose wall, typically built up 
 of a series of sculptured and perforated plates. Oil is usually 
 formed as the product of anabolism, even in forms possessing 
 pyrenoid-like bodies, but in a few cases starch is produced. Most 
 of the Peridiniales have yellow or brown or (in some freshwater 
 species) green chromatophores, usually numerous and band or 
 rod-like and radially arranged, but sometimes these are absent or 
 represented by leucoplasts — these colourless forms are mostly 
 saprophytic or in some cases holozoic, while Dogiel (41) and 
 Chatton (21, 22) have recently shown that certain forms are 
 
 c 
 
34 
 
 Flagellata and Primitive Algce 
 
 parasitic on various animals. Reproduction takes place by division 
 into two or more daughter cells (spores or zoogonidia) and resting 
 cysts are also formed by rejuvenescence of the cell contents. 
 However, the life cycle of very few forms has yet been worked out, 
 
 PHAEOPHYCEAE 
 
 Pleurocladla 
 
 Phaeotheimnion 
 
 PhaeocysLis 
 
 Naegellella Pyrocysteae 
 
 Phaeococcus and other 
 
 Phaeoplax Phytodlnlaceae 
 
 Perldinlaceae 
 
 with numerous flagella and reticulate chromatophore 
 
 / \ 
 
 C HL AM YDOM ON ADS 
 POL YBLEPHARIDS 
 
 CHLOROMONADS 
 
 Autotrophic M u 1 1 1 c 1 1 1 a - 1 1 k e 
 
 M a s t 1 g a m oe b o 1 d AncestorB 
 
 Table C. — Suggested Phylogeny of Brown Flagellate and Brown Algal 
 Scries, For details see Text, 
 
The Peridiniales and their Relationships, 35 
 
 despite the voluminous literature that has accumulated as the result 
 of the collection of plankton Peridiniales, at all times of the year, 
 by numerous workers ; there is, for instance, no proof at present 
 that a sexual process occurs in the ^I’oup — unless w'e include in it 
 the genus Noctiliica (see below). Zederbauer (157) observed 
 individuals of Ceratimn Hirundhiella^ a freshwater species, grouped 
 in pairs and connected by protoplasm, while the contents of other 
 individuals had been extruded in the form of a cyst — whence he 
 inferred that zygospores had been formed as the result of a 
 conjugation process. However, Jollos (62) and Wesenberg-Lund 
 (145) observed the formation of similar cysts in Ceratium which 
 had certainly arisen without copulation, and it would appear that 
 the paired cells seen by Zederbauer had arisen as the result of 
 abnormal cell division or that the process may be simply one of 
 plastogamic fusion such as occurs in certain Protozoa. 
 
 Schiitt (134) divided the Peridiniales into three families — 
 Gymnodiniaceae, Prorocentraceae, and Peridiniaceas. In the 
 Gymnodiniaceae the cell is naked or clad only by a thin mucilaginous 
 or cellulose wall showing uniform structure and in most cases 
 forming merely a delicate periplast like that of the majority of 
 Flagellata. Of the two flagella, one is directed backwards in the 
 longitudinal groove (sulcus) while the other (usually thrown into 
 undulating curves) lies in the transverse groove (annulus). Both 
 sulcus and annulus may be straight, meeting at right angles at one 
 point where the flagella arise — in this case the annulus is either 
 subequatorial (complete in Gyinnodinium, a half-ring in Hemidiniuni) 
 or is near the anterior pole so that the anterior (prje-annular) 
 portion of the cell is much smaller than the posterior and is rostrum- 
 like (Ainphidinium) \ or the annulus may be spirally coiled and the 
 sulcus slightly {Spiro diniuni) or markedly (Cochlodmium, Poicchetia) 
 spiral also, meeting the annulus at both ends, with the transverse 
 flagellum inserted at the anterior end of the annulus and the 
 longitudinal flagellum at the posterior end of the sulcus — Pouchetia 
 is distinguished from Cochlodinium by having a complicated 
 stigmatic apparatus consisting of a red or black pigmented body 
 with one or more large spheroidal refractive lens-like bodies 
 adjoining it. In this family Schiitt includes Pyrocystis (see below). 
 
 In the Prorocentraceae (Fig- 3) there is a shell consisting of 
 two biconvex valves, dotted with pores except on either side of the 
 suture ; from an opening in this suture, at the anterior end of the 
 cell, arise the flagella, of which one is directed forwards while the 
 second either vibrates about the base of the first or is directed 
 laterally. In the three genera included here by Schiitt, there are 
 usually two large plate-like chromatophores, one lying within each 
 valve of the wall, but sometimes these are deeply lobed or even 
 divided into a number of radiating elongated chromatophores, as 
 in the majority of Peridiniales. In Cenchridium the pore from 
 which the flagella arise is continued inwards as a gullet-like tube; 
 in Exuvicella and, more markedly, in Prorocentrum, there are small 
 projections of the wall close to the flagellum pore, which Schiitt 
 suggests may represent the beginnings of the characteristic wing- 
 like expansions of the margins of the flagellum groove in the 
 Peridiniaceae. 
 
Flagellata and Primitive Alga, 
 
 56 
 
 The remaining Peridiniales are placed by Schiitt in the family 
 Peridiniacese, in which the shell differs from that of the Proro- 
 centraceae in having a series of girdle plates intercalated between 
 the two valves. The girdle consists essentially of a narrow ring- 
 like plate with a groove (annulus) for the transverse flagellum, and 
 a pair of plates (sometimes each divided into several plates) placed 
 at right angles to this and containing the longitudinal groove (sulcus). 
 Each valve consists of two or more polar plates, which are either 
 joined directly to the girdle series or are separated by intercalary 
 
 Fig. 8. PROROCENTRACE.E. — 1, 2, Haplodinium antjoliense Klebs : 1, surface 
 view ; 2, side view ; 3, Cenchridium glohosum (Williams) Stein. 4, 5, Amphidinium 
 operculation Clap, et Lach. ; 4, ventral view, showing the flagella; 5, dorsal 
 view, showing nucleus and chromatophores. 6 to 10, Exuvialla marina Cienk. : 
 6 and 7, two aspects at right angles to each other, showing the flagella and 
 the surface markings of the shell ; 8 and 9, optical sections corresponding 
 respectively with 6 and 7, and showing the nucleus, chromatophores, pyrenoids, 
 and contractile vacuoles ; 10, empty valves of the shell, after escape of encysted 
 contents. 11 and 12 Provocentrum micans Ehrb., two views at right angles. 
 Chr., chromatophore ; c.v., contractile vacuole; nucleus ; pyrenoid, 
 1, 2, 8, 9, 10, from Klebs ; 3, 4, 5, from Stein ; 6, 7, 11, 12, from Schiitt. 
 All somewhat diagrammatic. 
 
 plates. The upper valve (epitheca) bears an apical pore, and in 
 most cases the sulcus is confined to the lower valve (hypotheca), 
 though sometimes it extends beyond the annulus right to the apex 
 of the cell {Steiniella^ Gonyaulax), or it may be short and extend 
 equidistantly on either side of the annulus {Protoceratiu>ii). Schiitt 
 divides the Peridiniacese into four sub-families — Glenodinieae (only 
 genus Glenodinium) ; Ptychodisceae (only genus Ptychodisctis)\ 
 Dinophyseae (six genera, including the most bizarre forms of 
 
The Peridiniales and their Relationships. 37 
 
 Peridiniales) ; and Ceratieae (Ceyatiiun^ PericVuiinni, etc. — this is 
 the largest division of the group). In the Dinophyseas the shell is 
 divided by a longitudinal suture into two subequal lateral portions ; 
 the epitheca is much smaller than the hypotheca, the borders of the 
 annulus are funnel-like and the left-hand border of the sulcus is 
 often developed into wings and spines. 
 
 According to Schiitt, the Peridiniaceae are connected with the 
 Gymnodiniaceae by the genus Glenodinutm, and with tlie Proro- 
 centraceae by the genus Ptychodiscus. In Glenodinium (Fig. 9, 9 to 
 13) the shell is thin and structureless (not sculptured or perforated), 
 and its differentiation into two valves and a girdle is only apparent 
 when rupture occurs at liberation of the encysted contents. In 
 Ptychodiscus the two valves have the same structure as in the 
 Prorocentraceas, but the girdle is represented by a thin soft 
 membranous ring-like band, while the sulcus is indicated by a 
 depression on one valve and a narrow plate on the other. 
 
 The results of recent work suggest considerable modifications 
 of Schiitt’s classification of the Peridiniales, and appear to afford a 
 basis for phylogenetic interpretations very different from those put 
 forward by that author in 1896. Our knowledge of the Peridiniales 
 and allied groups has been greatly extended in recent years by the 
 work of Apstein (1, 2), Borgert (13), Chatton (21, 22), Dogiel (41), 
 Jollos (62), Klebs (68), Kofoid (71, 72), Lemmermann (75-85), 
 Lohmann (86-88), Schilling (127, 128), and others ; the literature 
 is cited by Pavillard (115) and in various other general works. 
 
 The view that the Peridiniales are related to the Flagellata 
 appears to have been first put forward by Bergh (4), who pointed 
 out the striking resemblances between Prorocoitrnm and the Crypto- 
 monads. Bergh also suggested that a form like Prorocentrum 
 might have given rise to the Dinophyseae, in which the transverse 
 groove is near the anterior end of the cell, and that the Ceratieae 
 are derived from the Dinophyseae by progressive shifting backwards 
 of this groove to an approximately median position. Biitschli (18), 
 on the other hand, considered that in the evolution of the Peri- 
 diniales shifting of the annulus had taken place from behind 
 forwards ; according to his interpretation of the structure of Provo- 
 centrum^ which is followed by Schiitt, the suture between the two 
 valves is horizontal, and the insertion of the flagella lateral. Bergh 
 and Biitschli agreed in regarding the simple shell-less Gymno- 
 diniaceae as derived by reduction from the typical shell-clad 
 Peridiniales, and various other writers have adopted this view, as 
 being a necessary consequence of the principle that the Peridiniales 
 are of monophyletic origin. 
 
 A much simpler interpretation is obtained if we regard the 
 suture in the Prorocentraceae as being longitudinal and as 
 corresponding with the longitudinal suture in the Dinophyseae, 
 which ought perhaps to be separated as a distinct family — the 
 higher Peridiniales (Schiitt’s Peridiniaceae) would then fall into two 
 families, Ceratiaceae and Dinopliysidaceae. Including the two 
 families recently founded by Klebs and by Chatton, the Peridiniales 
 as a whole may be regarded as forming two distinct series, which 
 it is here suggested are of independent origin from the Cryptomonads. 
 
38 Plagellata and Primitive Algce. 
 
 The Gyninodiniaceae (Hig. 9) may well liave arisen from a 
 Cryptomonad like Protochrysis, with two unequal flagella arising 
 from a lateral depression having the form of an incomplete trans- 
 verse groove. In the Gymnodiniaceae, however, there are numerous 
 chromatophores instead of two, and the nucleus, as pointed out by 
 Klebs (68) has a characteristic fibrillar structure apparently not 
 found in the Chrysomonadineae. But granting these differences, 
 and the absence of what may be strictly regarded as transitional 
 
 Fig. 9. Gy.mnodinjace.^. — 1, Hemidinhim nasiitum Stein, showing flagellum 
 grooves, flagella, nucleus, and numerous small chromatophores. 2, Gymno- 
 dinium bogoriense Klebs. 3 to 8, Gymnodinium rotundatum Klebs: 1, two cysts 
 enclosed in the membrane of the parent cell ; 2, rupture of cyst shown on the 
 left in preceding figure, to set free the two motile cells ; 5, motile cell ; 6, the 
 
39 
 
 The Peridiniales and their Relationships, 
 
 same gradually coming to rest and about to lose its flagella ; 7, the same after 
 loss of flagella, secreting a drop of mucilage for attachment ; 8, the same, two 
 days later (the transverse furrow which had disappeared on coming to rest 
 has now been re-formed). 9, 10, Glenodinium piilvisculus Ehrb. : in 10 one of the 
 shell-valves has been forced off to allow escape of the spore, which soon 
 afterwards undergoes division. 11 to 13, Glenodinium emarginatum Klehs : in 11 
 the cell contents have undergone oblique longitudinal division ; 12 shows 
 escape of contents as a spore (cyst), and 13 the division of this cyst. 14, 
 Spirodiniim spirale (Bergh) Schutt. 15, 16, Cochlodinium styangulatum Schlitt. 
 17, Pouchetia fusus Schutt, showing the spirally coiled flagellum grooves, and 
 the stigma (consisting of a pigment-body with a refractive lens-like body on 
 either side of it. 18, 19, Polykrikos auricularia Butschli : in 18 the longitudinal 
 flagellum groove, eight transverse grooves, four nuclei, and five trichocysts ; 
 
 19, a trichocyst. 20 to 26, Cystodininm bataviense Klebs : 20, cyst with Peridinean 
 body ; 21 to 23, stages in division of cyst contents into two cells, which escape 
 by gelatinisation of one side of the cyst (seen in 24) ; 25, motile cell ; 26, motile 
 cell has become a cyst, set free by rupture of the cell- wall ; the black fleck in 
 
 20, 22, and 25 is a stigma (“ eye spot ”). 27 to 34, Diplodinium lunula (Schutt) 
 
 Klebs (= Pyrocystis lunula Schutt) : 27, uninucleate primary cyst; 28, cyst with 
 four nuclei, the cytoplasm not yet divided ; 29, cyst with four cells, each about 
 to divide again ; 30, sickle-shaped secondary cyst ; 31, contraction of contents 
 of same ; 32, 33, division of contents into motile Gymnodinium-like cells, of 
 which one is shown more highly magnified in 34. 35 to 40, Hypnodinium 
 
 spharicum Klebs; 35, a cell in optical section, showing the central nucleus, the 
 numerous small chromatophores in the peripheral and radiating portions of 
 the cytoplasm, an “eye spot,’’ and five orange-red oil drops; 36, cell with 
 rounded off contents showing Gymnodinium-like grooves; 37, stage in division, 
 showing two nuclei, two transverse grooves, and two “ eye spots’’ ; 37, division 
 into two Gymnodinium-like cells completed ; 39, 40, rupture of cyst, setting free 
 the two daughter cells, which have now lost their grooves. 
 
 1, 9, 10, from Stein ; 2 to 8, 11 to 13, 20 to 26, 35 to 40, from Klebs ; 14 to 
 17, from Schutt; 18, 19, from Bergh. 
 
 forms, there appears to be little doubt that the discovery of 
 Protochrysis has at any rate lessened the gap between the Crypto- 
 monads and a simple Peridinean genus like Hemidinium with its 
 incomplete transverse groove. From a form like Hemidinhuii, the 
 transition is easy to Gymnodininm and to Glenodinium (which is 
 best placed in the Gymnodiniaceae and which forms a connecting 
 link with the Ceratiaceae). These simple Gymnodiniacese form a 
 central group from which diverge lines leading in various directions. 
 In Spirodiniunit Cochlodinium^ and Pouchetia the cell is elongated 
 and the grooves spirally coiled, and the pigmented body (stigma) 
 found in the simpler forms is accompanied in Pouchetia by one or 
 more lens-like bodies. In Pouchetia armata (Dogiel, 41) the ceil is 
 provided with nettling organs (trichocysts) consisting of a conical 
 capsule containing a coiled stinging thread. Nettling organs of this 
 kind are also found in the remarkable naked holozoic genus 
 Polykrikos (Butschli, 18; Koloid, 72), in which the elongated body 
 has eight transverse grooves and a single straight longitudinal groove, 
 and there are eight nuclei — according to Delage (37) these are 
 meganuclei, accompanied by smaller nuclei (micronuclei) as in 
 Ciliate Infusoria, and each transverse groove has a flagellum. 
 From Kofoid’s account of Polykrikos, it would appear that the 
 apparently single cell is a colony of individuals arranged in a linear 
 series, owing to incomplete separation after division; Dogiel (41) 
 has described specimens with four transverse grooves and a single 
 nucleus. Polykrikos may be definitely placed in the Gymnodiniacese, 
 since the presence of nettling organs in Pouchetia connects it with 
 Cochlodinium and Spirodinium and thus with the simpler genera 
 
40 
 
 Plagellata and Primitive Algce. 
 
 like Gymnodiniuin. Whether Folykvikos forms a link between the 
 Peridiniales and the Ciliate Infusoria is, of course, an open question 
 in the absence of further transitional types. It is possible that the 
 genus Evythropsis (Hertwig, 57 ; Delage, 37 ; Pavillard, 114) affords 
 such a transition ; in this organism the irregularly spherical body 
 shows a longitudinal groove, a transverse groove with a wavy 
 flagellum at the anterior end of the body, and a relatively thick 
 contractile outgrowth at the posterior end, while there is a stigmatic 
 apparatus comparable with that of Pouchetia, Hertwig regarded 
 Evythropsis as an Infusorian allied to Vorticella ; while Metchnikoff 
 compared its appendage to the sucker of Acineta and placed the 
 genus in the Suctorial Infusoria. It is probable that the resemblances 
 to Infusoria presented by Polykrikos and Evythropsis are merely 
 superficial or due to homoplasy ; in any case, both genera appear 
 to be directly related to the Gymnodiniace^. 
 
 The life cycle of the lower Gymnodiniacese, so far as known, 
 is extremely simple. In some cases division occurs in the motile 
 condition, but more usually after encystment, the cyst being covered 
 by gelatinous envelopes or by a firm wall and its contents dividing 
 into two or more cells. In Cystodinium (Fig. 9, 20-26) the motile 
 cells resemble Gymnodinmm in structure, but on becoming encysted 
 they acquire an elongated and horned form, the contents then 
 become rounded off and dividing to produce two or four motile cells. 
 In Diplodinium (Fig. 9, 27-34) the life cycle is somewhat complicated, 
 since the encysted cell divides to form sixteen secondary cysts, each 
 of which gives rise to four, eight, or sixteen motile Gymnodmium-\ike 
 cells ; to this genus Klebs refers Pyvocystis lunula and certain 
 species which had previously been placed in the genus Gymnodiiiium» 
 Finally, Hypnodinium (Fig. 9, 35-40) is known only in the resting 
 stage ; on becoming encysted, the protoplast shows Gymnodinium- 
 like grooves and divides into two naked cells exactly like Gynino- 
 dinium but without flagella — on being set free by rupture of the cyst 
 these two cells acquire a membrane and soon form new cysts. 
 
 In the genera Blastodinium and Apodinium, recently discovered 
 by Chatton (21, 22), and perhaps best placed in a family (Blasto- 
 diniacese) distinct from but closely allied to the Gymnodiniaceae, 
 which live as parasites or commensals in the bodies of Copepods 
 and other marine animals, the cell divides into two portions, of 
 which one continues the ordinary vegetative cycle while the other 
 divides into a number of cysts which are set free as biflagellate 
 Gymiiodinium-Wke cells. 
 
 The genus Diplodinium leads from the GymnodiniaceaB to the 
 family Phytodiniacese (Fig. 10, 1-13), which includes the old genus 
 Pyvocystis (minus Pdunula, now transferred to the genus Diplodinium) 
 and four new genera founded by Klebs (68). In this family the 
 cells show Peridinean cytological features, though no grooves are 
 present; reproduction takes place by simple division of the cell 
 contents into two, but no motile cells have been observed. The 
 simplest form is Phytodininm, with ovoid cells (Fig. 10, 1,2); in 
 Pyvocystis (Blackman, 8) the protoplasm is radially arranged, and 
 is massed together at one end of the cell, very much as in the 
 primary cyst of Diplodinium lunula; in Tetvadinium (Fig. 10, 3-7) 
 
4 ^ 
 
 The Peridlniales and their Relationships. 
 
 the cell is tetrahedral, with two pointed processes at each angle ; 
 in Stylodinium (Fig. 10, 5, 9) the oval or spherical cell is attached 
 to a substratum by means of a gelatinous stalk ; while in Glceodinmm 
 
 Fig. 10. Phytodiniace^ (1 to 13), Cystoflagellata (14 to 16), and 
 vSilicoflagellata (17 to 21). 
 
 1, 2, Phtvodinium simplex Klebs : in 1 the cell has divided, in 2 the nucleus 
 is shown. 3 to 7, Tetvadinium javanicum Klebs : 3, cell showing vacuolate 
 cytoplasm, nucleus, an oil-drop, and numerous peripheral chromatophores ; 
 4, empty cell, showing all four angles ; 5, cell attached to a root-hair of Azolla ; 
 6, division ; 7, escape of the two daughter-cells from ruptured cyst-wall. 8, 
 9, Stylodinium globosum Klebs : 8, stalked cell attached to a root-hair of Azolla ; 
 9, escape of undivided contents by rupture of old cell-wall. 10 to 13, 
 Glceodinium montanum Klebs : 10, cell with several gelatinous envelopes derived 
 from older membranes; 11, division of the nueleus ; 12, cell division; 13, 
 older colony surrounded by gelatinous envelopes. 14, Noctiluca miliaris Suriray : 
 side view (optical section), showing on the left the short flagellum inserted in 
 the “ pharynx,” at the base of the thiek tentacle. 15, 16, Leptodiscus Hertwig : 
 15, surface view, ventral side, showing on the right a wide depression with 
 striated walls and on the left the narrow tube containing the flagellum; 16, 
 side view (optical section). 17 to 19, Distephanus speculum Stohr : 17, cell 
 showing skeleton and cell-contents (nucleus, cytoplasm, chromatophores) ; 
 18, 19, two views of skeleton. 20, Monaster rete Schiitt ; side view, showing 
 the two flagella arising from equatorial groove, and the internal skeleton. 
 21, Amphitolus elegans Schiitt : side view, showing the elaborate skeleton. 
 
 1 to 13, from Klebs; 14 to 19, from Delage ; 20, 21, from Schiitt. 
 
42 
 
 Plagellata and Primitive Algct. 
 
 (Fig. 10, ]0-13)i the most Alga-like form, colonies of considerable 
 size are formed by repeated division within a thick stratified 
 gelatinous investment. 
 
 The Noctilucaceae' (Cystoflagellata) are probably derived from 
 Pyrocystis-\\\iQ Peridiniales. In Noctihica (Fig. 10, 14) the spherical 
 cell shows great resemblance in internal structure to PyrocystiSt 
 though there is no cell-wall and there are, on the other hand, some 
 elaborations not found in Fyvocystis — e.g., the thick tentacle which 
 is transversely striated and shows movements, the short flagellum 
 in the gullet-like opening guarded by two projections (“tooth ” and 
 “ lip ”). The reproduction of Noctiluca is a somewhat remarkable 
 process — after conjugation of two cells budding occurs, and from 
 the buds there arise motile cells which show Gymnodinium-Wko. 
 features — a transverse groove (without flagellum, however) and on 
 the concave ventral side a backwardly directed longitudinal 
 flagellum. The other genera of the family — Leptodiscus (Fig. 10, 
 15, 16) and Cvaspedotella (Kofoid, 71) — also show specialised 
 structure, and do not serve to All the gap between Noctiluca and 
 Pyrocystis] in Leptodiscus the cell has the form of a watch-glass, 
 the convex ventral surface having a wide gullet-like depression on 
 one side, and on the other and a narrow pit containing a flagellum, 
 while Craspedotella resembles a medusa in form. 
 
 Reference has already been made to a possible connection 
 between Gymnodiniacese and the Infusoria. Certain organisms 
 are also known which appear to lead from the Peridiniales to 
 another group of Protozoa — the Radiolaria. The flagellated spores 
 produced by various Radiolaria (for details and some of Brandt’s 
 figures of these, see Gamble’s account of this group in Lankester’s 
 Treatise on Zoology, 151) present an extraordinarily close 
 resemblance to Gymnodiniiun and other simple Peridiniales, and 
 suggest the origin of this Protozoan group from Gyninodininm-WkQ 
 ancestors. Moreover, Schutt has described three genera which 
 appear to form direct links between Gymnodiniaceae and simple 
 Radiolaria, and which also suggest the possible origin of the 
 Diatoms; these genera {Gymnastev, Monaster, Amphitolus) have an 
 internal skeleton which recalls that of Radiolaria, and the body is 
 divided into two portions by an equatorial suture, which in 
 Amphitolus (Fig. 10, 21) and Monaster (Fig. 10, 20) is grooved, 
 while in Monaster the resemblance to Peridiniales is enhanced by 
 the presence of two flagella inserted in this groove and springing 
 laterally from the body. In addition, Borgert has shown that 
 certain genera — Distephanus (Fig. 10, 17-19), Mesoscena, Dyctiocha^ 
 Cannopilus — which had been previously placed in the Radiolaria 
 (in the bodies of which they live as commensals, and with which 
 they agree in having a siliceous skeleton) are Flagellate forms, for 
 whicli he formed the group Silicoflagellata (see also Lemmermann, 
 80, 83) ; these organisms have a skeleton consisting of transverse 
 rings which are either free or joined up by longitudinal spicules to 
 form a network, and in the genera named there is a single flagellum 
 (Borgert’s new genus Ebria has two flagella), while the protoplasm 
 contains numerous yellow chromatophores. The Silicoflagellata 
 may have been derived from forms like Monaster, or they may have 
 come from Chrysomonadinean ancestors — certain Chrysomonads 
 
The Peridlniales and their Relationships. 
 
 4 .^ 
 
 siiovv a tendency to the formation of flinty skeletons 
 Cluysosphcerella). The Coccosphaei'ales (Coccolithoplioridae, 83, 86, 
 87) are perhaps derived from simple Chromulinales ; in general 
 morphology they resemble forms like Chyysococcns, but with a 
 peculiar armour consisting of calcareous plates instead of a 
 homogeneous perisarc and suggesting comparison with the tesse- 
 lated siliceous armour of Mallomonas, though until their cytology 
 has been elucidated their affinities must remain in doubt. 
 
 In connexion with the Ci’yptomonads, mention may be made 
 of two remarkable and somewhat aberrant Flagellate genera 
 recently discovered by Scherffel,’ the position of which in the 
 scheme of classification above outlined appears to be doubtful. In 
 one of these forms, Mononiastix, there are two large laterally placed 
 green chromatophores, each with a pyrenoid, and starch is formed ; 
 the cell shows dorsiventral symmetry and there is a single terminal 
 flagellum. The other genus, Plenroniastix, is also a dorsiventral 
 form, but has brown chromatophores and produces oil and probably 
 also leucosin ; it too has a single flagellum, inserted laterally at the 
 obliquely truncate anterior end of the body. Scherffel inclines to 
 the view that Monomastix belongs to the Polyblepharidacea^, but 
 Pascher (in reviewing Scherffel’s paper in Zeitschv.f. Bot., Bd. 5, 
 1913, p. 405) considers that its affinities lie rather with the 
 Cryptomonads ; both writers refer Pleurowastix, somewhat doubt- 
 fully, to the Chrysomonads. The most remarkable character 
 common to these genera, apart from the possession of a single 
 flagellum (all hitherto described Cryptomonads and Chloromonads 
 have two flagella, though one order of Chrysomonads, the 
 Chromulinales, is characterised by a single flagellum) is the presence 
 of peculiar structures somewhat resembling the trichocysts found 
 in some Chloromonads (Rliaphidoiuonas, MerotricJia) and Peridiniales 
 {Polykrikos, see above) as well as in the Ciliate Infusoria. These 
 trichocyst-like organs, especially well developed in the green form 
 Monomastix, consist of a highly refractive outer layer and a less 
 refractive central mass which on treatment with various reagents 
 is protruded rapidly as a filament (in Plenvomastix usually as a 
 distinctly tubular structure). According to Scherffel, the structure 
 of these organs in the two new Flagellates confirms the suggestion 
 put forward by Kiinstler that the peculiar granular organs found 
 lining the gullet-like depression in the Cryptomonad body represent 
 rudimentary trichocysts. Among the Ciliate Infusoria correspond- 
 ing organs occur, in addition to more highly organised trichocysts, 
 and it appears probable that in both cases structures of this kind 
 are not always to be regarded as defensive organs but may be 
 merely products of secretion. Apart from its possession of pyrenoids 
 and starch, Monomastix might well be placed in the Chloromonads, 
 but on the whole it would appear that both genera may be perhaps 
 best classed provisionally among the Cryptomonads — as here 
 treated, this is a somewhat varied and generalised one, with many 
 divergent affinities. 
 
 ’ “ Zwei neue trichocystenartige Bildungen fiihrende Flagellaten.” 
 Arch. f. Protistenk., Bd. 27, 1912, pp. 94-128. 
 
44 
 
 Flagellata and Primitive Algce. 
 
 IX. — Conclusion. 
 
 W HILE the recent work summarised liere has led, through the 
 discovery of interesting new species and genera and the 
 re-investigation of forms previously known imperfectly, to a clearer 
 knowledge of the Brown Flagellates and of the relations between 
 these and the Brown Algpe, it has thrown little further light upon the 
 phylogeny of the Green Alga?. The possibility that the Cryptomonads 
 are related to the Chlamydomonads has been discussed by Fritsch 
 (46), who admits, however, that the origin of the flagella from a 
 depression and the obliquity of the cell in the Cryptomonads is 
 against the view of a really close relationship. However, the 
 Chrysomonadineae and the lowest Chlamydomonads — the Polyble- 
 
The Peridiniales and their Relationships. 45 
 
 pharidaceae — may well have arisen from a common ancestral form, 
 which we may imagine to have been multiflagellate and amoeboid, 
 with a basin-shaped chromatophore. Apart from the differences 
 in flagellum number and the nature of the assimilate we fiind corres- 
 ponding simple “ mastigamoeboid ” forms in each of the orders of 
 Chrysomonadineae — e.g., Chrysamceha, Hymenomonas, Ochromonas, 
 Wysotzkia\ while the Chloromonad genus suggests the 
 
 origin of the Chloromonadineae from a similar ancestral form by 
 the division of the primitively single basin-shaped chromatophore 
 into a number of small chloroplasts. If the multiflagellate condition 
 is taken as primitive, we must regard the Polyblepharidaceae, which 
 also have a limited power of change of shape, as being nearer to the 
 ancestral stock than any of the other coloured Flagellate and lower 
 Algal forms. 
 
 The nearest approach to such an ancestral form is the colourless 
 MttUicilia, with two species, of which M. lamstris is multinucleate 
 while M. marina has a single nucleus ; in both species, the spherical 
 body bears numerous radiating flagella, food is ingested by 
 pseudopodia which may be put out from any point, there are numerous 
 peripheral contractile vacuoles, and division occurs by median 
 constriction of the body as in Amceba. Probably the primitive form 
 of chromatophore was a reticulate peripheral sheet immediately 
 within the periplast, and when the flagella became restricted to the 
 anterior end of the body this sheet would become basin-shaped 
 (i.g., open anteriorly) as in the majority of Volvocales and in various 
 Chrysomonads, or on the other hand broken up into numerous small 
 chromatophores, as in Chloromonadineae, Glceomouas (allied to 
 Chlamydomonas), Chrysococcus dokidophorus (Chromulinales), etc. 
 A reticulate chromatophore occurs in Chrysapsis (one of the most 
 primitive Chrysomonads), and in certain Volvocales {Sphcsrella, 
 Chlorogonium). The bell-shaped chromatophore which is character- 
 istic of the Volvocales and of the simpler Chrysomonadineae has 
 undergone longitudinal splitting in at least one genus (Scherffelia) 
 in the former group and in the majority of the Chrysomonadineae, 
 giving rise to two lateral curved band-like chromatophores ; these 
 two types of chromatophore may occur in different species of the 
 same genus, as is seen in Uroglenopsis (Ochromonadales). 
 
 If, while bearing in mind Vuillemin’s timely caution against 
 dogmatism in such matters, we assume that autotrophic organisms 
 are primitive and heterotrophic organisms derived, and that the 
 Flagellata represent the most primitive organisms known to us, the 
 striking parallism which has been shown to exist between the Brown 
 Flagellates and certain colourless Flagellates suggests the view 
 that the whole of the latter may have arisen from coloured autotropic 
 forms by adaptation to heterotrophic modes of nutrition. On this 
 view, the classification of the Flagellata which has hitherto been 
 accepted is purely physiological, and therefore artificial, correspond- 
 ing with the conventional division of the Thallophyta into Algae and 
 Fungi ; and the various groups of colourless Flagellates will doubtless 
 be shown, on further investigation, to have arisen from correspond- 
 ing forms among the coloured Flagellates, just as the various groups 
 of Fungi are now regarded as arising from corresponding Algal 
 forms. Of the many lines starting from a hypothetical autotrophic 
 Multicilia-\ike ancestral form, with a reticulate chromatophore, 
 
46 
 
 Flagellata and Primitive Algce. 
 
 numerous peripherally situated nuclear bodies, and numerous 
 flagella, some have ended blindly and produced nothing higher than 
 Flagellates — a few of these remaining autotrophic but the majority 
 becoming adapted to various modes of heterotrophic nutrition — 
 while three may be traced into the Vegetable Kingdom and lead 
 respectively (i) through the Polyblepharids to the Chlamydomonads 
 and thence to the majority of Green Algae, (ii) through the Chloro- 
 monads to the Confervales, and (iii) through the Chrysomonads to 
 the Cryptomonads and thence to the Phseophyceae, the Peridiniales, 
 and probably the Diatoms. 
 
 The origin of the remaining Algal groups from Flagellata is 
 much more difficult to trace, owing to the absence of transitional 
 forms. There are no forms whatever which would serve to connect 
 the Blue-green and the Red Algae with the known Flagellates of 
 corresponding colour; it is much more likely that the Cyanophyceae 
 are related to the Bacteria, while the Rhodophyceae may have been 
 derived from the same stock as the Dictyotaceae, which occupy a 
 somewhat isolated position among the Phaeophyceae. The origin of 
 the Diatoms is an equally open question ; it seems likely, at any 
 rate, that they are related to the Peridiniales or to the Chryso- 
 monads rather than to the Conjugatae. 
 
 LITERATURE REFERRED TO. 
 
 The following list of literature on the Flagellata and Primitive Algae is not 
 intended to be exhaustive. Reference should be made to the literature lists 
 given by Biitschli (18), Calkins (19), Delage (37), Doflein (40), Fritsch (46), 
 Klebs (67, 68), Lotsy (89), M’Keever (91), Minchin (93), Oltmanns (95), Pascher 
 (101), Pavillard (114), Scherffel (125), Schiitt (134), Senn (135), Stein (138), 
 \Ville (149, 150), Willej’ and Hickson (151). 
 
 1. Apstein, C. “Die Pyrocysteen der Plankton-Expedition.” Wiss. 
 
 Ergebnisse d. Plankton-Exp. d. Humboldt-Stiftung, 
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 2. ,, Pyrocystis lunula und ihre Fortpflanzung.” Wiss. 
 
 Meeresunters., Kiel, N.F.Bd. 9, 1906. 
 
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 d. deutsch. bot. Ges., Bd. 23, 1905, pp. 159-161. 
 
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 Bd. 7, 1881. 
 
 5. Bergon, P. “ Les processes de division, de rajeunissement de la cellule, 
 
 et de sporulation chez le Biddulphia mobiliensis Bailey.” 
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 6. Blackman, F. F. “ The primitive Algae and the Flagellata.” Annals of 
 
 Botany, vol. 14, 1900. 
 
 7. Blackman, F. F., and Tansley, A. G. “A revision of the classification 
 
 of the Green Algae.” New Phytologist, vol. 1 , 1902. 
 
 8. Blackman, V. H. “ Observations on the Pyrocysteae.” New Phyto- 
 
 logist, vol. 1, 1902, pp. 178-188. 
 
 9. Bohlin, K. “ Zur Morphologie und Biologie einzelliger Algen.” Oefvers. 
 
 K. Vet. Akad. Forhandl., 1897, pp. 507-527. 
 
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 Borzi.” Bih. t. K. Sven. Vet. Akad. Handl., Bd. 23, 
 Afd. 3, 1897 (Summary in Bot. Centralbl., Bd. 73, 
 1898, p. 213). 
 
 11. ,, “ Utkast till de grona algernas och archegoniaternas 
 
 fylogeni.” Upsala, 1901 (Summary in Bot. Centralbl., 
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 12. Borgert, A. “ Ueber die Dictyochiden.” Zeitschr. fiir wiss. Zoologie, 
 
 Bd. 51, 1891. 
 
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 ,, “ Cyrtophoya, eine neue tentakeltragende Chrysomonade aus 
 
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 ,, “ Zwei braune Flagellaten.’’ Ibid, Bd. 29, 1911, pp. 190-192. 
 
 ,, “ Ueber die B^ziehungen der Cryptomonaden zu den Algen.” 
 
 Ibid., Bd. 29, 1911, pp. 193-203. 
 
 ,, “Marine Flagellaten im Sussvvasser.” Ibid., Bd. 29, 1911, 
 
 pp. 517-523. 
 
 ,, “ Ueber Nannoplankton des Susswassers.” Ibid., Bd, 29, 
 
 1911, pp. 523 533. 
 
 ,, “ Scherpfelia, eine neue Chlamydomonadine.” Lotos, Natur- 
 
 wiss. Zeitschr., Prag, Bd. 59, 1911, pp. 341-3. 
 
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 1912, pp. 274-287. 
 
 ,, “ Eine farblose rhizopodiale Chrysomonade.” Ber. d. 
 
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 ,, “Ueber Rhizopoden-und Palmellastadien bei Flagellaten 
 
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 25, 1912, pp. 153 200. 
 
 ,, “ Braune Flagellaten mit seitlichen Geisseln.” Zeitschrift 
 
 f. wiss. Zoologie, Bd. 100, 1912, pp. 177-189. 
 
 ,, “ Die Heterokontengattung PseudotetraMron.” Hedwigia, 
 
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:/ 
 
 
 ADDENDUM. 
 
 URING the publication of the foregoing series of papers, two 
 
 interesting new members of the Volvocales have been 
 
 discovered and described, and as the descriptions of these forms 
 came to the writer’s notice too late for reference in the portion 
 dealing with this group, a note concerning them is here appended. 
 
 West^ has described under the name Scourfieldia complanata a 
 form which bears exactly the same relationship to Chlamydomonas 
 that Scherffelia does to Carteria. This organism has a' strongly 
 compressed body, with two long flagella springing from the notched 
 “anterior” end (in progression the organism moves backwards, 
 however) ; the single chloroplast is sub*campanulate but flattened 
 and has no pyrenoid ; there is no stigma (“ eye-spot,”) and the life 
 history is unknown. 
 
 Korschikoff- gives the name Spermatozopsis exsultans to an 
 organism which apparently belongs to the Polyblepharidaceae, 
 bearing much the same relationship to Pyraniimonas that Chloromonas 
 does to Chlamydomonas — for instance there is no pyrenoid. The 
 body is capable of undergoing considerable “ euglenoid ” changes of 
 shape, but is typically elongated and spirally twisted through nearly 
 a whole turn; the posterior end is usually pointed, while the 
 anterior end is rounded and bears four long flagella, or in some 
 cases two only. The greater part of the body is occupied by the 
 chloroplast, which lies on the convex side and usually extends to 
 both ends of the body, though ki some cases it is curved at the 
 posterior end, while at the anterior end there is a well-marked 
 “ eye-spot” ; there is no pyrenoid. No trace of a cell-wall could be 
 detected, and the organism is apparently capable of greater 
 “ metabolic ” changes of form than have been observed in any other 
 member of the Polyblepharidaceae. From the other members of 
 the latter family Spermatozopsis differs in being bilaterally sym- 
 metrical, with a unilateral chloroplast, though in this respect it 
 agrees with some of the Chlamydomonads — e.g., Chlamydomonas 
 media and C. parietaria. Vegetative reproduction was observed to 
 occur in the same manner as in Pyraniimonas, consisting in longi- 
 tudinal division into two daughter cells and taking place in the 
 motile state. 
 
 ’ West, G. S. “Algological Notes.” Journal of Botany, 1912, pp. 
 321-331. 
 
 2 Korschikoff, A. '* Spemiatozopsis exsultans nov. gen. et sp. aus der Gruppe 
 der Volvocales.” Ber. d. deutsch. hot. Ges., Band 31, 1913, pp. 174-183.