CELLULAR STRUCTURE 35 
We see here a simple example of co-ordination 
between the cells of an organism. It is true 
that it is of a very rudimentary kind, but 
the fact that an organism, originating in this 
manner, possesses a definite form at all, is 
a clear proof of its existence. 
The form of Apiocystis seems to be fairly 
constant, but when conditions are suitable, 
some or all of the protoplasts may escape 
from the gelatinous sheath and swim away 
as biciliate Chlamydomonas-like organisms, 
though they are destitute, for a time at least, 
of even a cell membrane. In this condition 
they are known as Zoospores ; when one of 
them settles down it becomes invested in a 
cell wall secreted by the protoplasm, and 
by repeated fission builds up another Apio- 
cystis plant. This mode of reproduction by 
means of zoospores is very common in the 
algze, and it serves to recall the early stages 
in the history of the race which is thus re- 
peated during the beginning of the life of a 
new individual. 
Now a pear-shaped organism is, by its 
very form, rendered incapable of reaching 
a large size, at any rate without such accessory 
complications as are not to be thought of in 
connection with primitive plants. There are 
other lines of development which have proved 
more fruitful from an evolutionary point 
of view, and of these the flattened expansion 
and the filamentous types represent the most 
successful. Indeed, it is on these lines, or 
