SEX IN PROTOZOA 201 



four. Tlic two larger cells are male and female gamonts each of which 

 is destined to give rise to eight gametes, the male line developing 

 faster than the female. The first division of the gamont is "gonial," 

 sho\\ing the diploid number of four chromosomes. During the sec- 

 ond division, which is heterotypic, reduction to two chromosomes 

 takes place. The third di\'ision is homeotypic, again, with hut two 

 chromosomes. 1 hus eioht marcrogamctes and eight slightly smaller 

 microgametes are formed. These fuse in pairs to produce eight zy- 

 gotes, each of which becomes a sporont and develops into a spore. 



Order Microsporidia 



In this group the spores are small, and in the majority there is 

 only one polar capsule or polar filament. The small size of many of 

 these organisms makes the study of their development difficult. Most 

 accounts in the literature are incomplete. 



In Thelohania legeri (Kudo, 1924a) young sporonts develop 

 as shown in Fig. X (5 to 9). A quadrinucleate stage (5), formed 

 after schizogony, divides into two binucleate cells (6). These undergo 

 division with both nuclei dividing at the same time (7, 8). In the 

 four binucleate cells so produced (8), nuclear fusion takes place 

 (9). The uninucleate sporonts thus formed proceed to the formation 

 of spores. In several other accounts Kudo has described autogamy in 

 connection with the development of the sporont, for example in 

 Thelohania opacita (1924b), Sternpella (Thelohania) inagjia (1925), 

 and Nosema aedis (1930), all parasitic in mosquitoes. Aleiosis is not 

 clearly indicated. 



Debaiseaux (1928) postulated two somewhat different patterns 

 of development, one for the polysporous and the other for the mono- 

 sporous Microsporidia. For the former, vegetative development may 

 be by binary fission or by plasmodium formation, but eventually a 

 special binucleate stage is reached. This divides by a peculiar type 

 of division to produce two binucleate cells within each of which 

 nuclear fusion takes place to produce a zygote. This becomes a spo- 

 ront and forms a spore (see Fig. X, 5 to 9). For the monosporous 

 forms a similar vegetative development ends likewise in a special 

 binucleate stage which undergoes the special type of division pro- 

 ducing two binucleate cells. In these cells nuclear fusion does not take 

 place until after spore formation. In Plistophora chironoiiii, Weiser 



