858 P R T Z O A [FLAGELLATA. simply to the parental form (Fig. XX. 23 to 26). In the Chlauiydotnonadina a single adult individual by division produces small individuals, so-called "microgoni Ha." These copulate with one another or with similar microgonidia formed by other adults (as iu Chlorogonium. Fig. XX. 7) ; or more rarely in certain genera a microgonidi im copulates with an ordinary individual (macrogonidium). 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 iu this case is the male element and equivalent to a spermatozoon ; the macrogonidium 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 produce by division microgonidia ; and, regarding the colony as a mnlticellular 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 microgonidia or spermatozoa of the male colonies. The differentiation of the cell-units of the colony into neutral or merely carrying cells of the general bod} 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 Knterozoa 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 Vorticellidai may be instructively compared with that of the Phytomastigoda ; see below.] Fam. 6. TETRAMITIXA. Symmetrical, naked, colourless, some what amoeboid 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- monai, Orassi ; Tfichomonas, Donne ; Trichomastix, Blochmann. Fam. 7. POI,YMASTIGIN T A. 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. GcnerA.Hexamihis, Duj. (Fig. XXI. 5) ; Megastoma, Grassi ; Polymastix, BiitschlL Fam. 8. TREPOMOXADIXA, Kent. As Polymastigina, but the lateral anterior flagella are placed far back on the sides. Genera.. Trepomonas, Duj., described recently without name bv Dallinger (67). Fam. 9. CRYPTOMON AntXA. 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. Cyathomonos, From. ; Chilom.onas, Ehr. ; Cri/ptomonas Ehr. ; Oxyrrhis, Duj. Fam. 10. LOPHOMOXADTXA. A tuft of numerous flagella an teriorlv. Genns.Lophomowis, Stein (Fig. XXI. 9, connects the Flage l- lata with the Peritrichous Ciliata). Sub-class II. Choanoflagellata, Saville Kent. Flagellata provided with an upstanding collar surroumlin" the anterior pole of the cell from which the single flagellum 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 (ProUrospongia). ORDER 1. NUDA, Lankester. Character*. Individuals naked, secreting neither a lorica (cup) nor a gelatinous envelope. Genera. Mowaiya, S. Kent (solitary stalked or sessile); Codo- nga, James Clark (united socially on a common stalk or pedicle, tig. iXL 3, 4) ; Astrosiga, S. Kent; Desmarella, S. Kent. ORDER 2. LORICATA, Lankester. Characters. ^ci individual collarod-cell unit secretes a horny cup or shell. J 15 FIG. XXI. Flagellata. 1. Salpingceca fusiformia, 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 vmbellata, Tateni ; one of the Choanoflagellata ; adult colony formed by dichotomous growth ; x C25. 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 a, nucleus, and b, contrac tile vacuole. 6, 7. Salpingceca urceolata, S. Kent ; one of the Choano flagellata ; 6, with collar extended; 7, with collar retracted within t -e stalked cup. a, nucleus; b, contractile vacuole. 8. Polytoma uvella, Mull. sp. ; one of the Phytoniaftigoda. a, nucleus ; b, contractile vacuole. x 800. 9. Lophomonas blattarum, Stein ; one of the Isomastigoda, from the intestine of Blatta orientalist, a, nucleus. 10. Bodo lens, Miill. ; one of the Ueteromastigoda; x 800. a, nucleus; b, contractile vacuole ; the wavy filament is a flagellum, the straight one is an immobile trailing thread. 11. Tetramitussulcatus, Stein; one of the Isomastigoda; x430. a, nucleus ; b, contractile vacuole. 12. Anthophysa wgetam, O. F. Miiller; 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 restrains, Perty; one of the Isomastigoda; x 1000. a, nucleus; b, con tractile vacuole. 15. Proterospongia Hacckdi, Saville Kent ; one of the Choanoflagellata ; x 800. A social colony of about forty flngellate
zooids. a, nucleus; b, contractile vacuole; c, aniboeiform zooid sunk