A fountain Alga. 79 
The escape of zoospores is best-observed in the palmelloid 
stage where the cells are not piled on one another. A single cell 
when watched in the act of forming zoospores, appears to lose the 
distinctness of its walls, until when the first sign of movement of 
the contained zoospores is observed, the walls seem to have dis¬ 
appeared. The contents divide into four, as said, and the ball of 
four zoospores begins to move slowly, turning over, and the 
zoospores may be seen writhing over one another. Their move¬ 
ments become more violent, and they begin to jerk rapidly about, 
and although nothing can be seen which prevents their becoming 
free, it is evident from their movements that they are still held 
fast in some way—probably by their cilia being imbedded in some 
mucus formed from the broken down cell. They finally become 
free, although one may be held fast for a considerable time after 
the others have departed. No remains of an envelope from which 
they have escaped can be seen. The time taken to become free 
from the first sign of movement is about five minutes. 
The zoospores (Fig. 11) are pear-shaped with two cilia at the 
anterior narrow end. The anterior end is colourless and clear, 
except for two colourless globules sometimes seen, which may be 
vacuoles. The posterior end contains the chloroplast, which is 
basin-shaped, and under a high power appears to consist of 
numerous oval chlorophyll granules. There is a well-marked red 
eye-spot in the posterior end. 
The zoospores differ slightly in size, but all appear to have the 
same morphological value— i.e., they all germinate into a new 
thallus without any conjugation. 
After swimming about vigorously for a short time occasionally 
being arrested through the cilia becoming entangled with diatoms, 
etc., the zoospore comes to rest, attaching itself by its front end 
to the coverslip, a diatom, or the edge of a thallus. The colourless 
anterior end bearing the cilia is immediately drawn up, so that the 
zoospore assumes a circular form and appears uniformly green— 
i.e., without any colourless portion (Fig. lib.) 
It commences to germinate immediately and in twenty-four 
hours has pushed out a short tube, which elongates rapidly, so that 
in forty-eight hours all the contents of the zoospore have passed 
into the germinating tube and the circular wall of the empty 
zoospore may be seen very clearly (Fig la). The green contents 
may be seen passing slowly out from the zoospore into the tube : 
This tube is the first filament and by lateral budding grows into the 
the thallus, from which again zoospores are formed. 
