146 Colonial Organisms. [ February, 
birth, and a significant indication of the origin of the latter, The 
sexual offspring of Volvox, however, is born as a single germinal 
cell. 
In the vegetable world the free cell colony assumes a size and 
complexity considerably in advance of any animal instances, for 
the Algæ and Fungi begin their external life as single cells. 
Thus, however large and complex they become, the process of 
growth is distinctly that of cell colonization. 
There is one important fact observable in all cell colonies. 
They do not display varying and indefinite expansion, but tend 
to assume specific forms. These organisms are probably results 
of natural selection, and possess the forms best adapted to the life 
conditions of the colony, which forms are hereditarily transmitted. 
Now we may readily conceive, in the numberless fluctuations of 
nature, the appearance of circumstances to which the mature col 
ony would be well adapted, but in which the germinal cell and 
the growing colony would be in danger of extirpation. Under 
such circumstances it would be a decided advantage if the germ 
could pass through its first stages of division within the maternal 
body, and a still more decided advantage if it could be retained 
under the maternal protection until sufficiently developed to be 
able to take care of itself in the ‘battle of life. Such, poss®” 
was the method in which the Protozoan cell colony became the 
Metazoan organism, namely, by the retention of the germ 
cell under the maternal protection until it had unfolded into 
self-sustaining organism. The degree to which this embryom® 
growth proceeds differs greatly in different cases. In al J 
the new creature is born as a single cell. In the Protozoan ©” 
ony it is shed into the external world at this stage. In the 
zoan it is retained until it has passed through a portion Of $ 
whole of its development, or, more usually, is born as an Ege 
which the germ rests in a store of nutriment provided DY 
mother, and enclosed within a protective covering. Only 19 3 
case of the Mammalia is the development completed before & 
ternal birth. 
Thus the division of the germinal cell, in the formation of a 
Morula, is in no fundamental sense different from the divisio? 
the ameeboid cell, in the formation of a colony of Forami™ 
The Flagellate colony, from which there is reason to believe ve 
the sponge originated, may, in the process of evolution, 5 
