CHYTEIDIINEAE 67 



The nuclei divide simultaneously by karyokinesis, 

 Fig. 16, d. Sexual stages were obtained by supplying 

 fresh food (ant larvae) to old cultures of Saprolegnia. The 

 sex-cells especially in O. saprolegniae and 0. luxurians are 

 easily distinguished from the vegetative cells by their 

 vacuolated coarsely granular plasm. All the contents of 

 the antheridium pass into the oogonium, Fig. 16, g and Ti, 

 from one to several hours being required. The nuclei of 

 the antheridium are small and in an active state, those of 

 the oogonium are large and resting. The ripe oogonium, 

 Fig. 16, i 9 has a thick endospore, inside this a finely granular 

 layer containing the nuclei, inside this again a coarsely 

 granular layer, and in the middle a large oil- drop, as in the 

 zygospore of Polyphagus. 



The staining reactions of the nuclei of the zygote vary 

 at different stages. 



Barrett did not see amoeboid changes in, nor fusions of, 

 the larger non-sexual parasites ; nor could he confirm 

 Fischer's view about an alternation of generations. 



Sphaerita endogena. This parasite was discovered in 

 a culture of Euglena viridis by Dangeard, who also described 

 another chytridian, Nudeophaga amoebae, considered below 

 in Chapter X. For biology the value of these two genera 

 consists in the light they shed on processes previously 

 supposed to be modes of reproduction in protozoa and 

 which are now known to be instances of parasitism. 



Sphaerita grows in the cytoplasm of its host, the nucleus 



