ALGAL AND FUNGAL PROTISTS 31 



water and transfer to tap water. Sporangia appear in 

 24 hours (Chamberlain). The thallus is normally an 

 undivided sac, simple in Saprolegnia, branched in Achlya. 

 Septa are formed to shut off reproductive organs or to 

 repair injury. 



In agamic reproduction the end of a filament swells as a 

 long sporangium, a septum isolating its contents, which 

 subdivide into many uninucleate segments. In Saprolegnia 

 these escape directly as bi-flagellate zoospores, in Achlya in 

 a mass held together by a jelly, Figs. 3 and 4. 



The large sporanges of Saprolegnia with their central 

 vacuole, cylindrical or irregularly linear, according to the 

 thickness of the protoplasm, lend themselves to the study 

 of the mode of origin of zoospores ; this has been described 

 by M. Hartog and others ; seeing that corresponding stages 

 are seen in Pythium and Chytridiineae, the leading features 

 may be enumerated, following E. J. Butler's account : 

 1, Preliminary separation of spore-origins by concentration 

 of protoplasm around each nucleus, linear vacuoles occupying 

 the intervals ; 2, homogeneous stage caused by swelling of 

 spore-origins and disappearance of the sporangial vacuoles ; 

 this stage has been explained as being due to rupture of the 

 skin-layer admitting water to the spore-origins ; 3, vacuo- 

 lation ; in the origins are formed a number of vacuoles, 

 which grow, fuse, and disappear ; discharging water into the 

 exterior where the escaped cell-sap attracts bacteria ; 

 4, final separation of zoospores by surface grooves meeting 



