SFX IN PROroZOA 



199 



host, wlicrc rlic rest of the development takes phice. Cirowth (2 to 

 5 ) is accompanied by nuclear divisions showing four chromosomes 

 (3). Further grow tli mav he accompanied by asexual reproduction 

 (6 to 10) or the production of spores (11 to 17). Kach trophic 

 individual becomes a pansporoblast (11 to 14) and produces two 

 spores (15, 16). All nuclear divisions show four chromosomes except 

 that (14), in which meiosis takes place, producing the gamete nuclei, 

 each with two chromosomes. The two haploid nuclei, show^n with 

 marginal endosomes, remain in the sporoplasm (15 to 17) while the 

 other nuclei, belonging to the "somatic" cells which produce the 

 valves of the sporocyst and the polar capules, eventually disappear. 



Fig. X. 



1-4, diagrammatic sequences of mitoses within a single sporoblast of a myxosporidian 

 (cf. Fig. W), from Noble (1944). iMeiosis in one nucleus at third division. 5-9, 

 nuclear history in sporogony of Thelohania legeri, from Kudo (1924a), including 

 nuclear fusion (9). 10-13, stages in sporogony of Haplosporidmvi IhnnodriU, from 

 Granata (1914); 10, gametes; 11, 12, fusion of gametes; 13, resulting spores. (All 

 illustrations redrawn.) 



