208 



PROTOZOOLOGY 



In the coccidian, Aggregata eberthi (Fig. 246), according to Dobell 

 (1925), Naville (1925) and Belaf (1926) and in the gregarine, Diplo- 

 cystis schneideri, according to Jameson (1920), there is no reduction 

 in the number of chromosomes during the gamete-formation, but the 

 first zygotic division is meiotic, 12 to 6 and 6 to 3, respectively. A 

 similar reduction takes place also in Actinocephalus parvus (8 to 4, 

 after Weschenf elder, 1938), Greg arina blattarum (6 to 3, after Sprague, 

 1941), Adelina deronis (20 to 10, after Hauschka, 1943), etc. Tri- 

 chonympha and other flagellates (p. 185) of woodroach, Polytoma 



Fig. 93. Degeneration or aging in Stylonychia pustulata. X340 (Maupas, 

 modified), a, Beginning stage with reduction in size and completely 

 atrophied micronucleus; b, c, advanced stages in which disappearance of 

 the frontal zone, reduction in size, and fragmentation of the macronucleus 

 occurred; d, final stage before disintegration. 



and Chlamydomonas (p. 276) also undergo postzygotic meiosis. 

 Thus in these organisms, the zygote is the only stage in which the 

 nucleus is diploid. 



Some seventy years ago Weismann pointed out that a protozoan 

 grows and muliplies by binary fission or budding into two equal or 

 unequal individuals without loss of any protoplasmic part and these 

 in turn grow and divide, and that thus in Protozoa there is neither 

 senescence nor natural death which occur invariably in Metazoa in 

 which germ and soma cells are differentiated. Since that time, the 

 problem of potential immortality of Protozoa has been a matter 

 which attracted the attention of numerous investigators. Because of 

 large dimensions, rapid growth and reproduction, and ease with 



