348 THE PROTOZOA 



The maturation of the female gamete does not necessarily take the form of 

 expulsion of the karyosomo ; on the contrary, the karyosome may be retained 

 throughout the development. In the macrogamete of Cydospora caryolytica 

 the nucleus divides twice to form two reduction-nuclei, which are cast off, 

 and a third nucleus which persists as the pronucleus. A similar reduction- 

 process has been described by Chagas in Adelea harlmanni. In Adelea ovata, 

 according to Jollos, a reducing division occurs in the female gametocyte before 

 association with the male takes place ; this is denied, however, by Schellack 

 and Reichenow and by Debaisieux. 



In Caryotropha the male sporont does not divide at once into microgametes, 

 but first into a number of microgametocytes, each of which then produces 

 microgametes. The process of gamete-formation is thus seen to be exactly 

 parallel to the schizogony, in which the schizont first divides into cytomeres, 

 which in their turn produce merozoites. It is obvious that in coccidia, as in 

 Protozoa generally, schizogony and gametogenesis are strictly homologous 

 processes ; the only difference, primarily, is in the nature and destiny of the 

 swarm-spores produced in each case, merozoites or gametes. This comparison 

 accentuates the fact, which will be discussed further below, that in the coccidia 

 multiple reproduction to produce gametes is entirely in abeyance in the 

 female sex. 



7. The fully-formed microgamete (Fig. 50, p. 102) is a minute, 

 slender, serpentine organism, the body of which consists almost 

 entirely of chromatin ; the cytoplasm is represented by the two 

 flagella, which arise close together at one end of the body. One 

 flagellum is entirely free, the other runs along the body to the hinder 

 end, from which it is continued freely ; thus the structure of the 

 male gamete recalls that of a trypanoplasm in the heterornastigote 

 arrangement of the flagella. 



The male gametes swarm round the inert female gamete, and one 

 of them penetrates into it and fertilizes it. As soon as the entrance 

 of a microgamete is effected, the macrogamete secretes a tough 

 membrane, the oocyst, at the surface of the body, preventing the 

 penetration of any other microgametes. A fertilization-spindle 

 (Fig. 69, p. 127 ; Fig. 152, J, K) is then formed in the zygote. The 

 female pronucleus becomes spread out into a fusiform figure con- 

 sisting of grains of chromatin on an achromatiiiic framework. When 

 the spindle is complete, the male pronucleus breaks up into granules 

 of chromatin which spread over the spindle, and are thus com- 

 mingled intimately with the chromatin of the female pronucleus. 

 When this has taken place, the spindle contracts to form the rounded 

 synkaryon, and the syngamy is complete. 



The structure of the microgamete varies in different species. In some 

 cases (Adelea, Klossia, Legerella, Barroussia spiralis) flagella are wanting, 

 and the microgamete is a slender, spirochsete-like organism, consisting entirely, 

 so far as can be seen, of chromatin, but actively motile. When fiagella are 

 present, they are usually two in number. In Orcheobius herpobdellce, Bar- 

 roussia (Minchinia) caudata, and some other species, the microgamete ter- 

 minates anteriorly in a point or rostrum, close behind which two flagella are 

 given off, and are directed obliquely backwards, quite free from the body. 

 In Aggregata, Moroff (94) describes the microgametes as long and slender, 

 with a nucleus of peculiar form, sometimes greatly drawn out, and with 



