MONOBLEPHARIDALES 711 



of fertilization observed was the body of the male gamete completely 

 absorbed by the ooplasm. There was always a small papilla-like part 

 which persisted at the apex and from which protruded the flagellum of 

 the antherozoid (Fig. 51 F). The remainder of the male gamete could 

 be detected for a time as a slightly more granular material in the anterior 

 part of the egg, but it was soon lost to view. Almost instantly after the 

 absorption of the major part of the antherozoid the papilla-like residue 

 of this structure on the surface of the egg started to increase in size 

 (Fig. 51 G). This marked the initiation of evacuation of the zygote from 

 the oogonium. More definite evidence of emergence could then be seen 

 in the migration of the conspicuous globules into the enlarging papilla 

 (Fig. 51 H-J). These continued to flow out with the cytoplasm of the 

 zygote. Meanwhile, the flagellum remained passive, but slowly assumed 

 a lateral position with respect to the orifice of the oogonium as the zygote 

 oozed out. The completely emerged zygote was at first rather pyriform, 

 with the flagellum nearly basal and extending at a right angle or more 

 to the long axis of the body (Fig. 51 K). The zygote rounded off, remain- 

 ed quiescent for a few seconds, and then began to rock gently (Fig. 51 L). 

 A trembling movement of increasing intensity was soon initiated, which 

 frequently carried the zygote somewhat away from the oogonial orifice. 

 Lateral vibration of the hitherto quiescent flagellum followed, and vacu- 

 oles appeared in the anterior part of the now more ovoid body. After a 

 few violent tugs, accompanied by rapid vibration of the dark-appearing 

 flagellum, the zygote began to rotate on its long axis as well as to pro- 

 gress forward; finally it swam slowly oil. Under poor environmental 

 conditions the zygote may fail to emerge, and the oospore is formed 

 in the oogonium. Cytological preparations of motile zygotes (Sparrow, 

 1953b) indicate that the nucleus of the male gamete (not a fusion 

 nucleus) presides over the activities of the flagellum. 



After a period of motility of unknown duration, frequently punc- 

 tuated by intervals of quiescence and strong amoeboid crawling, the 

 zygote comes to rest. Its flagellum is apparently absorbed and it is 

 surrounded by a thickened wall. The globules persist for a time, but 

 eventually these are assimilated and the oospore undergoes a period of 

 dormancy, far removed from the oogonium. The two gamete nuclei 

 remain distinct at least in the early stages of oospore maturation. In 



