200 SEX IN MICROORGANISMS 



Figure X (1 to 4) shows diagrammatically the sequence of 

 mitoses within a single sporoblast, according to Noble (1944). At 

 the end of nuclear division in each sporoblast there are six nuclei, 

 two of which are sister haploid nuclei, the other four belonging to 

 the somatic cells as explained above. George vitch (1935, 1936) 

 reached a similar conclusion in regard to the life cycles of Myxospori- 

 dia in general, with the exception that he believed that meiosis takes 

 place in two nuclei during the final nuclear divisions, one haploid 

 product of each division degenerating like a polar body. If the inter- 

 pretations of Georgevitch and Noble truly represent the life cycles 

 of the Myxosporidia, then the cycles are relatively simple. However, 

 there is much disagreement in the extensive literature on the group, 

 but only one more example will be cited. 



Naville has contributed a series of reports on this group besides 

 providing a general review in his monograph (1931). In his study 

 oi Sphaeromyxa sabrazesi (1930a) along with other Myxosporidia, he 

 described meiosis in cells segregated from the general protoplasm of 

 the trophozoite. There are two kinds, larger (female) and smaller 

 (male). By two meiotic divisions, the larger cell produces two "polar 

 bodies" and the smaller gives rise to four equal small haploid cells. 

 A smaller haploid cell unites with a larger one without nuclear fusion 

 to constitute a pansporoblast which produces two spores. Thus all 

 nuclei in the sporoblast are haploid according to this interpretation. 

 In other respects the process of spore formation is similar to that of 

 Ceratomyxa blennius (Fig. W.) More detailed studies are needed to 

 reevaluate these more complicated life cycles, described by many 

 authors, in the light of the interpretations of Georgevitch (1935, 

 1936) and of Noble (1944). 



Order Actinoiny xidia 



The spores of members of this order are somewhat like those 

 of the Myxosporidia but have ternary symmetry with three sporocyst 

 valves and three polar capsules. There are a number of descriptions 

 of life cycles, but only one will be mentioned. According to Naville 

 (1930b), in Giiyenotia sphaeriilosa early trophic stages are always 

 binucleate but the origin of the nuclei is obscure. After growth and 

 nuclear division, two large rounded cells are surrounded by a proto- 

 plasmic membrane containing two nuclei, which may increase to 



