CHLOROPHYCEA 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 Volvocinee (fresh water) suggests inevitable 
speculations which may easily be made too much of. 
In the allied genus Derbesia (Codiacew) 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 segmenia- 
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 
