32 PROTISTS AND DISEASE 



newly-formed linear vacuoles, which re-appear in the 

 protoplasm. 



In Saprolegnia the zoospores leave the sporangium as 

 motile egg-shaped bodies like those of algae, Fig. 4, C, a. 

 They have two flagella at their narrow end which is foremost 

 in progression, and three vacuoles in the granular plasm. 

 After a few minutes the zoospore comes to rest, its form 

 changes to a sphere and a cell-wall of cellulose is secreted. 

 After some hours or even days the contents escape again as 

 a zoospore, this time kidney-shaped like those of Achlya. 

 The second mobile stage may be omitted, the spore germi- 

 nating directly as a hypha. 



This transformation in the zoospores of Saprolegnia is 

 termed " diplantish " byde Bary, suggesting that at different 

 stages the zoospores gave the impression that they belonged 

 to two different plants. The somewhat consonant term 

 " diplanetism " is now applied to the same phenomenon, 

 signifying a double period of motility. 



In Dictyucus the zoospores instead of escaping from the 

 sporangium in one mass are retained in the sporangium 

 where they germinate and escape by penetrating the 

 sporangium wall, or, failing in this, they perish, the fate 

 of the majority. 



Resting conidia. In old growths, especially of Sapro- 

 legnia, the thick hyphae break up transversely into segments, 

 which are cylindrical, round, or barrel-shaped. These seg- 

 ments are resting conidia ; they are rich in protoplasm and 



