q 
1884. | Colonial Organisms. 147 
gained a somewhat complex organization, protected by fibrous 
and mineral secretions. Perhaps primitively yielding its germs 
as free cells, to develop into colonies externally, it may, in the 
exigencies of the struggle for existence, have come to retain 
them until they had developed into organized colonies, capable 
of selfsupport. Yet during the long period in which these 
gradual changes took place, the cells of the sponge colony con- 
tinued to retain the characteristics of the Amcebz and the Flagel- , 
lata, so that to-day they display the double character of a colony 
of Protozoa and of a Metazoan individual. 
We have dwelt at considerable length on this one case, as it 
involves the principle at the basis of all organic development. 
There is one other matter of interest connected with it to which 
_ We may here refer. The retention of the embryo within the ma- 
ternal body, or within the egg, has an important bearing on the 
question of evolution. This latter retention is a true “ accelera- 
tion of development.”! The embryo, while thus retained, is spe- 
cially favored in its growth. Provided with food without per- 
Sonal exertion, as in the case of free cell colonization, none of its 
energies are exhausted, and that organic development which is 
So greatly favored by complete rest proceeds rapidly. Its condi- 
tion resembles that of the insect in the pupa stage, in which, sup- 
Plied with abundant nutriment, and in a state of complete rest, 
organic development is rapidly attained. Such is the case with 
the embryo within the egg or the maternal womb. Its develop- 
ment is strongly accelerated, its larval stages passed through so 
rapidly that many of them are slurred over, and only the more 
marked stages are discoverable, and the new individual, when at 
length forced to depend on its own exertions, begins its free life 
ata much higher stage than in the case of the germ that is shed 
mito the external world as a single cell, or a very immature 
ny. 
If now We come to the consideration of Metazoan colonies, 
eon a gradual variation from simple to complex conditions 
“Y analogous to the parallel case of cell colonies. Many of 
aaa of the Metazoa are nearly as simple as those of the 
the Such is the case with the Ascidia and the Polyzoa. 
. + Colonies are compounds of precisely similar, asexually-born 
viduals, each of which pursues life as an individual, though 
: 1G 
Pe. Origin of Genera. 1868. 
