CHLOROPHYCE.E 131 



each portion becomes a zoospore. The zoospore 

 retains the character of its parent cell in respect of 

 a cell-sap cavity, traversed by threads of protoplasm. 

 A certain resemblance of this remarkable body to 

 the Volvocinece (fresh water) suggests inevitable 

 speculations which may easily be made too much of. 

 In the allied genus Derbesia (Codiacece) there are 

 formed a number of zoospores in each zoosporangium 

 but before this the parent cell contains a large 

 number of nuclei which unite with each other, and 

 thus become reduced to a number equivalent to the 

 number of zoospores. 



The zoospores soon lose their cilia and settle down, 

 becoming invested with a cell-membrane. They do 

 not rest, however, more than a day or two at most, 

 and germinate by the emission of one or more tubes. 

 It happens in some species that antheridia and 

 oogonia are occasionally formed on these filaments 

 immediately after germination. 



Motionless spores are produced by the formation of 

 cross-walls near the apex and the abstriction of this 

 portion, which first swells into an oval or globular 

 form. It secretes a new cell-wall, and is set free by the 

 dissolution of the original wall. In some cases such 

 spores germinate soon, in most they rest before 

 germinating. This spore-formation, like the more 

 extensive formation of such bodies by segmenta- 

 tion of the thallus, is often caused by injury or 

 unfavourable external conditions, and is more charac- 

 teristic of the species inhabiting fresh water, which 

 are moreover subject to the attack of rotifers 

 (Notommata) giving rise to galls. 



K 2 



