REPRODUCTION AND THE LIFE CYCLE 183 



multiplication is binary division of the trophozoite, as found among 

 the schizogregarines, where, as in ophryocystis, according to Leger 

 ('07), vegetative increase may be by simple division, as in ameba. In 

 other cases, however, the nucleus of the organism divides repeatedly 

 until many are present, when the cell divides into as many schizozoites 

 or merozoites as there are nuclei (Fig. 76). Schizogony becomes 

 more complicated in other genera of schizogregarines, where, as in 

 Eleutheroschizon (Brasil, 1906) or in Schizocystis (Dogiel), a process 

 of internal budding similar to that in suctoria (acineta, tokophrya, 

 etc.) takes place. In the former, a parasite of the marine annelid 

 Scoloplos armiger, Brasil ('06), has shown that the nucleus multiplies 

 by mitosis until many are present, when each is surrounded by a small 

 part of the protoplasm and all remain in the trophozoite, which acts as 

 nurse (Fig. 76, A-D). Similarly, in Schizocystis sipunculi, a parasite 

 of Sipuncidii-s nudus, Dogiel ('07), described the formation of a brood 

 pouch with many merozoites (Fig. 76, E-G), and, as in the preceding 

 form, the nurse cell or parent trophozoite is finally discarded as an 

 empty shell. 



Processes like these would seem to be less primitive than simple 

 division, more primitive than merozoite formation in the coccidiidia, 

 where the entire cell is utilized in the formation of such asexual spores; 

 a further stage leading to full schizogony is illustrated by another 

 gregarine selenidium, in which, according to Brasil ('07), the entire 

 protoplasmic contents of the cell are used in merozoite formation. 

 These methods of increase have probably arisen from simple division 

 in response to the environmental conditions, and the resulting germs, 

 like sister cells from division, are produced by simultaneous division 

 of the entire cell. Such asexual spores are never protected by chitinous 

 coverings, and for this reason have been called gymnospores, as the 

 equivalent of merozoites and as distinctive from the covered spores or 

 chlamydospores, of the sexual generation. In some rare cases, e. g., 

 in Legerella nova among the coccidiidia, the sporozoites, like mero- 

 zoites, are naked. 



In still other cases among the coccidiidia endogenous multiplication 

 is further complicated by the division of the trophozoite into frag- 

 ments ("cytomeres" of Siedlecki), each of which becomes the centre 

 of merozoite formation. Such further complications are characteristic 

 of Klossiella viuris (parasite of the mouse) and Caryotropha mesnili, 

 a parasite of the germinal cells of the annelid Polymnia nehulosa. 

 The highest type undoubtedly occurs in those forms of coccidiidia, 

 where merozoite formation accompanies the permanent differentiation 

 of the sexes, where, as in Cyclospora caryolytica (parasite of the mole), 

 Adelea ovata (parasite of the centipede), a series of male and female 

 merozoites are produced, which give rise to male and female tropho- 

 zoites, and these, finally, to sexually differentiated gametocytes. 



