Sporozoa 3 1 3 



cycle or may develop directly into sporoblasts. The trophozoite of the 

 large polysporous Myxosporida usually becomes a plasmodium (Fig. 6. 

 26, F) without intervening reproduction. The size of the mature tropho- 

 zoite varies considerably in different species but lengths of 100-500pi. are 

 not uncommon. 



frS 





Fig. 6. 27. A. Young trophozoite with a single nucleus, Leptotheca ohlma- 

 cheri; xl880 (after Kudo). B. Binucleate trophozoite, Ceratomyxa shasta 

 Noble; the more heavily stained nucleus will gi\e rise to sporoblastic nuclei, 

 the other will become the somatic residual nucleus; x2160 (after N.). C-F. 

 Leptotheca nhlmacheri (after Kudo): C. Trophozoite with eight sporoblastic 

 nuclei and a lightly stained somatic residual nucleus. D. Trophozoite with 

 two sporoblasts; in each, two cystogenous "cells" lie at the periphery in a 

 dense zone of cytoplasm; somatic residual nucleus lies outside the sporoblasts. 

 E. Later stage in the development of spores; the development of polar 

 capsules from each pair of capsulogenous "cells" is under way; nuclei of the 

 cystogenous "cells" lie in the denser peripheral cytoplasm; the nuclei of the 

 sporoplasms are surrounded by vacuolated cytoplasm; C-E, xl880. F. Mature 

 spore with two polar filaments and two sporoplasms; xl200. 



The growth phase often ends with the appearance of sporoblasts. How- 

 ever, growth continues during the production of spores in polysporous 

 genera such as Myxidium (98). Although there are reports to the contrary, 

 the most conclusive recent evidence (97, 98, 99) indicates that the sporo- 

 blast or pansporoblast is not the result of syngamy or plasmogamy. In 

 typical sporulation, certain "cells" in the trophozoite become differen- 



