PROTOZOA 



29 



simply to the parental form (Fig. XX. 23 to 26). In the 

 Chlamydomonadina a single adult individual by division produces 

 small individuals, so-called "microgonidia." These copulate with 

 one another or with similar microgonidia formed by other adults 

 (as in Chlorogonium, Fig. XX. 7) ; or more rarely in certain 

 genera a microgonidium copulates with an ordinary individual 

 (maerogonidium). The result in either case is a " zygote," a cell 

 formed by fusion of two which divides in the usual way to produce 

 new individuals. The microgonidium in this case is the male 

 element and equivalent to a spermatozoon ; the maerogonidium is 

 the female and equivalent to an egg-cell. The zygote is a fertilized 

 egg-cell, or oo-spermospore. In the colony-building forms we find 

 that only certain cells produee by division microgonidia ; and, 

 regarding the colony as a multicellular individual, we may consider 

 these cells as testis-cells and their microgonidia as spermatozoa. 

 In some colony-building forms the microgonidia copulate with 

 ordinary cells of the colony which, when thus fertilized, become 

 encysted as zygotes, and subsequently separate and develop by 

 division into new colonies. In Volvox the macrogonidia are also 

 specially -formed cells (not merely any of the ordinary vegetative 

 cells), so that in a sexually ripe colony we can distinguish egg- 

 cells as well as sperm mother-cells. Not only so, but in some 

 instances (Eudorina and some species of Volvox) the colonies which 

 produce sexual cells can not merely be distinguished from the 

 asexual colonies (which reproduce parthenogenetically), but can be 

 distinguished also inter se into male colonies, which produce from 

 certain of their constituent cell-units spermatozoa or microgonidia 

 only, and female colonies which produce no male cells, but only 

 macrogonidia or egg-cells which are destined to be fertilized by 

 the microgouidia or spermatozoa of the male colonies. 



The differentiation of the cell-units of the colony into neutral or 

 merely carrying cells of the general body on the one hand and 

 special sexual cells on the other is extremely important. It places 

 these cell-colonies on a level with the Enterozoa (Metazoa) in 

 regard to reproduction, and it cannot be doubted that the same 

 process of specialization of the reproductive function, at first com- 

 mon to all the cells of the cell-complex, has gone on in both 

 cases. The perishable body which carries the reproductive cells is 

 nevertheless essentially different in the two cases, in the Volvocina 

 being composed of equipollent units, in the Enterozoa being com- 

 posed of units distributed in two physiologically and morphologi- 

 cally distinct layers or tissues, the ectoderm and the endoderm. 



The sexual reproduction of the Vorticellidse may be instructively 

 compared with that of the Phytomastigoda ; see below.] 



Fam. 6. TETRAMITINA. Symmetrical, naked, colourless, some- 

 what ama;boid forms, with four flagella or three and an undulating 

 membrane. Nutrition animal, but mouth rarely seen. 



Genera. Collodictyon, Carter ; Tetramitus, Perty (Fig. XXI. 

 11, 14 ; calycine monad of Dallinger and Drysdale (66)) ; Monocerco- 

 monaa, Grassi ; Trichomonas, Donne ; Trichomaslix, Blochmann. 



Fam. 7. POLYMASTIOINA. Small, colourless, symmetrical forms. 

 Two flagella at the hinder end of the body and two or three on each 

 side in front. Nutrition animal or saprophytic. 



Genera. Hexamitus, Duj. (Fig. XXI. 5) ; Megastoma, Grassi ; 

 Polymastix, Biitschli. 



Fam. 8. TREPOMONADINA, Kent. As Polymastigina, but the 

 lateral anterior flagella are placed far back on the sides. 



Genera. Trepomonas, Duj., described recently without name by 

 Dallinger (67). 



Fam. 9. CRYPTOMOXADINA. Coloured or colourless, laterally 

 compressed, asymmetrical forms ; with two very long anterior 

 flagella, placed a little on one side springing from a deep atrium- 

 like groove or furrow (cf. Dinoflagellata and Noctiluca, to which 

 these forms lead). 



Genera. Cyathomonas, From. ; Chilomonas, Ehr. ; Cryptommas, 

 Ehr. ; Oxyrrhis, Duj. 



Fam. 10. LOPHOMONADINA. A tuft of numerous flagella anteriorly. 



Genus. Lophomonas, Stein (Fig. XXI. 9, connects the Flagel- 

 lata with the Peritrichous Ciliata). 



Sub-class II. Choanoflagellata, Saville Kent. 



Flagellata provided with an upstanding collar surrounding the 

 anterior pole of the cell from which the single flagelium springs, 

 identical in essential structure with the "collared cells " of Sponges. 

 Single or colony-building. Individuals naked (Codosiga), or inhabit- 

 ing each a cup (Salpingceca), or embedded in a gelatinous common 

 investment (Proterospongia). 



ORDER 1. NUDA, Lankester. 



Cltaracters. Individuals naked, secreting neither a lorica (cup) 

 nor a gelatinous envelope. 



Genera. Monosiga, S. Kent (solitary stalked or sessile) ; Codo- 

 siga, James Clark (united socially on a common stalk or pedicle, 

 Fig. XXI. 3, 4) ; Astrosiga, S. Kent ; Desmarella, S. Kent. 



ORDER 2. LORICATA, Lankester. 



Characters. Each individual collared-cell unit secretes a horny 

 cup or shell. 



FIG. XXI. Flagellata. 1. Salpingaeca fusiformis, S. Kent ; one of the 

 Choanoflagellata. The protoplasmic body is drawn together within the 

 goblet-shaped shell, and divided into numerous spores, x 1500. 2. 

 Escape of the spores of the same as monoflagellate and swarm-spores. 

 3. Codosiga umbellata, Tatem ; one of the Choanoflagellata ; adult colony 

 formed by diehotomous growth ; x 625. 4. A single zooid of the same ; 

 x 1250. a, nucleus ; 6, contractile vacuole ; c, the characteristic " collar" 

 formed by cuticle on the inner face of which is a most delicate network of 

 naked streaming protoplasm. 5. Hexamita inflata, Duj. ; one of the 



Isomastigoda ; x 650 ; normal adult; showing o, nucleus, and ft, contrac- 

 tile vacuole. 6, 7. Salpingoeca urceolata, S. Kent ; one of the Choano- 

 flagellata ; 6, with collar extended ; 7, with collar retracted within the 

 stalked cup. a, nucleus ; b, contractile vacuole. 8. Polytoma uvella, 

 Mull. sp. ; one of the Phytomastigoda. a, nucleus ; b, contractile vacuole. 

 x 800. 9. Lophomonas blattarttm, Stein ; one of the Isomagtigoda, 

 from the intestine of Blatta orientalis. a, nucleus. 10. Bodo lens, Mull. ; 

 one of the Heteromastigoda; x 800. a, nucleus; b, contractile vacuole ; 

 the wavy filament is a flagelium, the straight one is an immobile trailing 

 thread. 11. Tetramitus suhatus, Stein; one of the Isomastigoda ; X430. 

 a, nucleus; 6, contractile vacuole. 12. Anthophysa vegetans, O. F. 

 MUller ; one of the Monadidea ; x 300. A typical, erect, shortly-branching 

 colony stock with four terminal monad-clusters. 13. Monad cluster of 

 the same in optical section (x 800), showing the relation of the 

 individual monads or flagellate zooids to the stem a. 14. Tetramitus 

 rostratus, Perty ; one of the Isomastigoda ; x 1000. a, nucleus ; b, con- 

 tractile vacuole. 15. Proterospongia Haeckeli, Saville Kent ; one of 

 the Choanoflagellata; x 800. A social colony of about forty flagellate 

 zooids. a, nucleus; b, contractile vacuole; c, ambceifomi zooid sunk 



