30 



PROTOZOA 



within the common jelly or test (compared by S. Kent to the mesoderm- 

 cells of a sponge-colony) ; d, similar zooid multiplying by transverse 

 fission ; e, normal zooids with their collars contracted ; /, hyaline mucila- 

 ginous common test or zoothecium ; g, individual contracted and dividing 

 into minute flagellate spores (microgonidia) comparable to the spermato- 

 zoa of a Sponge. 



Genera. Salpingceca, James Clark (sedentary, Fig. XXI. 6, 7) ; 

 Lagenosca, S. Kent (free swimming) ; Polyosca, S. Kent (cups united 

 socially to form a branching zoeecium as in Dinobryon). 



ORDER 3. GELATINIGERA, Lankester. 



The cell-units secrete a copious gelatinous investment and form 

 large colonies. 



Genera. Phalansteriwn, Cienk. (Fig. XX. 12) ; Proterospongia, 

 Saville Kent (Fig. XXI. 15). 



[The Choanoflagel lata were practically discovered by the Ameri- 

 can naturalist James Clark (68), who also discovered that the ciliated 

 chambers of Sponges are lined by collared cells of the same peculiar 

 structure as the individual Choanoflagellata, and hence was led to 

 regard the Sponges as colonies of Choanoflagellata. Saville Kent 

 (69) has added much to our knowledge of the group, and by his 

 discovery of Proterospongia (see Fig. XXI. 15, and description) 

 has rendered the derivation of the Sponges from the Flagellata a 

 tenable hypothesis.] 



Further remarks on the Flagellata. Increased attention has 

 been directed of late years to the Flagellata in consequence of the 

 researches of Cienkowski, Biitschli, James Clark, Saville Kent, and 

 Stein. They present a very wide range of structure, from the 

 simple amoeboid forms to the elaborate colonies of Volvox and 

 Proterospongia. By some they are regarded as the parent-group 

 of the whole of the Protozoa ; but, whilst not conceding to them 

 this position, but removing to the Proteomyxa those Flagellata 

 which would justify such a view, we hold it probable that they are 

 the ancestral group of the mouth-bearing Corticata, and that the 

 Ciliata and Dinonagellata have been derived from them. One 

 general topic of importance in relation to them may be touched on 

 here, and that is the nature of the flagellum and its movements. 

 Speaking roughly, a flagellum may be said to be an isolated filament 

 of vibratile protoplasm, whilst a cilium is one of many associated 

 filaments of the kind. The movement, however, of a flagellum is 

 not the same as that of any cilium ; and the movement of all 

 flagella is not identical. A cilium is simply bent and straightened 

 alternately, its substance probably containing, side by side, a con- 

 tractile and an elastic fibril. A flagellum exhibits lashing move- 

 ments to and fro, and is thrown into serpentine waves during these 

 movements. But two totally distinct kinds of flagella are to be 

 distinguished, viz., (a) the pulsellum, and (b) the tractellum. An 

 example of the pulsellum is seen in the tail of a spermatozoon which 

 drives the body in front of it, as does the tadpole's tail. Such 

 a "pulsellum" is the cause of the movement of the Bacteria. It 

 is never found in the Flagellata. So little attention has been paid 

 to this fact that affinities are declared by recent writers to exist 

 between Bacteria and Flagellata. The flagellum of the Flagellata 

 is totally distinct from the pulsellum of the Bacteria. It is carried 

 in front of the body and draws the body after it, being used as a 

 man uses his arm and hand when swimming on his side. Hence 

 it may be distinguished as a "tractellum. Its action may be 

 best studied in some of the large Euglenoidea, such as Astasia. 

 Here it is stiff at the base and is carried rigidly in front of the 

 animal, but its terminal third is reflected and exhibits in this 

 reflected condition swinging and undulatory movements tending to 

 propel the reflected part of the flagellum forward, and so exerting a 

 traction in that direction upon the whole animal. It is in this way 

 (by reflexion of its extremity) that the flagellum or tractellum of 

 the Flagellata also acts so as to impel food-particles against the base 

 of the flagellum where the oral aperture is situated. 



Many of the Flagellata are parasitic (some hsematozoic, see Lewis, 

 70); the majority live in the midst of putrefying organic matter in 

 sea and fresh waters, but are not known to be active as agents of 

 putrefaction. Dallinger and Drysdale have shown that the spores 

 of Bodo and others will survive an exposure to a higher tempera- 

 ture than do any known Schizomycetes (Bacteria), viz., 250 to 

 300 Fahr., for ten minutes, although the adults are killed at 180. 



CLASS III. DINOFLAGELLATA, Butschli. 

 Characters. Corticate Protozoaof a bilaterally asymmetricalform, 

 sometimes flattened from back to ventral surface (Diplopsalis, 

 Glenodinium), sometimes from the front to the hinder region 

 (Ceratium, Peridinium), sometimes from right to left (Dinophysis, 

 Amphidinium, Prorocentrum) the anterior region and ventral 

 surface being determined by the presence of a longitudinal groove 

 and a large flagellum projecting from it. In all except the genus 

 Prorocentrum (Fig. XXII. 6) there is as well as a longitudinal 

 groove a transverse groove (hence Diuifera) in which lies horizon- 

 tally a second flagellum (Klebs and Butschli), hitherto mistaken for 

 a girdle of cilia. The transverse groove lies either at the anterior 

 end of the body (Dinophysis, Fig. XXII. 3, 4 ; Amphidinium) or 



at the middle. In Gymnodinium it takes a spiral course. In 

 Polykrikos (a compound metameric form) there are eight indepen- 

 dent transverse grooves. 



The Dinoflagellata are either enclosed in a cuticular shell 

 (Ceratium, Peridinium, Dinophysis, Diplopsalis, Glenodinium, 

 Prorocentrum, &c. ) or are naked (Gymnodinium and Polykrikos). 

 The cuticular membrane (or shell) consists of cellulose or of a 

 similar substance (cf. Labyrinthulidea) and not, as has been sup- 

 posed, of silica, nor of chitin-like substance ; it is cither a simple 

 cyst or perforated by pores, and may be built up of separate plates 

 (Fig. XXII. 10). 



The cortical protoplasm contains trichocysts in Polykrikos. 



The medullary protoplasm contains often chlorophyll and also 

 diatomin and starch or other amyloid substance. In these cases 

 (Ceratium, some species of Peridinium, Glenodinium, Prorocentrum, 

 Dinophysis acuta) nutrition appears to be holophytic. But in 

 others (Gymnodinium and Polykrikos) these substances are absent 

 and food-particles are found in the medullary protoplasm which 

 have been taken in from the exterior through a mouth ; in these 

 nutrition is holozoic. In others which are devoid of chlorophyll 

 and diatomin, &c., there is found a vesicle and an orifice connected 

 with the exterior near the base of the flagellum (cf. Flagellata) by 

 which water and dissolved or minutely granular food-matter is 

 introduced into the medullary protoplasm (Protojieridinium pellu- 

 cidmn, Peridinium divergens, Diplopsalis lenticula, Dinophysis 

 lasvis). It is important to note that these divergent methods of 

 nutrition are exhibited by different species of one and the same 

 genus, and possibly by individuals of one species in successive 

 phases of growth (?). 



No contractile vacuole has been observed in Dinoflagellata. 



The nucleus is usually single and very large, and has a peculiar 

 labyrinthine arrangement of chromatin substance. 



Transverse binary fission is the only reproductive process as yet 

 ascertained. It occurs cither in the free condition (Fig. XXII. 2) 

 or in peculiar horned cysts (Fig. XXII. 8). Conjugation has been 

 observed in some cases (by Stein in Gymnodinium). 



Mostly marine, some freshwater. Many are phosphorescent. 



The Dinoflagellata are divisible into two orders, according to the 

 presence or absence of the transverse groove. 



ORDEII 1. ADINIDA, Bergh. 



Characters. Body compressed laterally; both longitudinal and 

 transverse flagellum placed at the anterior pole ; a transverse groove 

 is wanting ; a cuticular shell is present. 



Genera. Prorocentrum, Ehr. (Fig. XXII. 6, 7); Exuviella, 

 C\Gi\\i.(Dinopyxis, Stein; Cryptomonas, Ehr.). 



ORDER 2. DINIFERA, Bergh. 



Characters. A transverse groove is present and usually a longi- 

 tudinal groove. The animals are either naked or loricate. 



Fam. 1. DINOPHYIDA, Bergh. Body compressed ; the transverse 

 groove at the anterior pole ; the longitudinal groove present ; 

 longitudinal flagellum directed backwards ; loricate. 



Genera. Dinophysis, Ehr. (Fig. XXII. 3, 4) ; Amphidinium, 

 Cl. & L. ; Amphisolenia, Stein ; Histioneis, Stein ; Citharistes, 

 Stein ; Ornithocercus, Stein. 



Fam. 2. PERIDINIDA, Bergh. Body cither globular or flattened ; 

 transverse groove nearly equatorial ; longitudinal groove narrow or 

 broad ; loricate. 



Genera. Protoperidinium, Bergh; Peridinium (Ehr.), Stein 

 (Fig. XXII. 1, 2); Protoceratium, Bergh ; Ceratium, Schrank (Fig. 

 XXII. 15) ; Diplo2)salis, Bergh ; Glenodinium, Ehr. ; Ileterocapsa, 

 Stein ; Gonyaulax, Diesing ; Goniodoma, Stein ; Blepharocysta, 

 Ehr. ; Podolampas, Stein ; Amphidoma, Stein ; Oxytoxum, Stein ; 

 Plychodiscus, Stein ; Pyrophacus, Stein ; Ceratocorys, Stein. 



Fam. 3. GYMNODINIDA, Bergh. As Peridinida but no lorica 

 (cuticular shell). 



Genera. Gymnodinium (Fig. XXII. 5), Stein ; Hemidinium, 

 Bergh. 



Fam. 4. POLYDINIDA, Butschli. As Gymnodinida, but with 

 several independent transverse grooves. 



Genus. Polykrikos, Butschli. 



Further Remarks on the Dinoflagellata. This small group is at 

 the moment of the printing of the present article receiving a large 

 amount of attention from Bergh (81), Klebs (83), and Biitschli (82), 

 and has recently been greatly extended by the discoveries of Stein 

 (80), the last work of the great illustrator of the Cilia te Protozoa 

 before his death. The constitution of the cell-wall or cuticle from 

 cellulose, as well as the presence of chlorophyll and diatomin, and 

 the holophytic nutrition of many forms recently demonstrated by 

 Bergh, has led to the suggestion that the Dinoflagellata are to be 

 regarded as plants, and allied to the Diatomacea? and Desmidiacere. 

 Physiological grounds of this kind have, however, as has been 

 pointed out above, little importance in determining the affinities 

 of Protozoa. Butschli (82) in a recent very important article has 

 shown in confirmation of Klebs that the Dinoflagellata do not 



