ALGAL AND FUNGAL PROTISTS 39 



minutes before the vesicle is formed. In the vesicle a rolling 

 of the contents is observed before subdivision, 



Zoospores are at first amoeboid then kidney-shaped with 

 2 flagella attached at the hilum. They escape by rupture 

 of the vesicle, and tend to collect at the surface of the water. 

 They become encapsuled before germination ; diplanetism 

 has been observed by Butler in one species. 



In most species germination is by a branched hypha, but 

 in P. tenue and others parasitic in Vaucheria, Spirogyra, 

 &c. the encysted zoospore having settled on a host filament 

 forms a penetration-tube like that of some olpidians. 



The gametangia, Fig. 6, d, and Fig. 7, consist of a round 

 oogonium and an antheridium which arises close to the 

 oogonium from the same hypha or from an adjoining hypha. 

 The tip of the antheridium touches the oogonium into 

 which it sends a process, the fertilisation canal, through 

 which in hanging- drop cultures the gonoplasm can be seen 

 to pass. 



The brooch-like arrangement of the gametangia is the 

 origin of the name of the group. Sometimes two or more 

 antheridia are attached to the same oogonium. 



Amoeba-like movements of the oosphere in the course 

 of preparation for fertilisation are described by Marshall 

 Ward, who observed that the passage of the antheridial 

 contents requires about an hour. The periplasm from 

 which the outer wall of the oospore is formed is scanty. 



The ripe oospore of Pythium after a long resting period 



