1884.] : Colonial Organisms. 145 
its nutrition and growth have become distinct from those of the 
mother. The only discoverable difference is that in the one case 
the nutriment is obtained independently of the mother, in the 
other case it is for a time provided by the mother. 
The phenomena succeeding birth are the same in both cases. 
Continued division of the germ cell takes place and a mass of 
cohering cells is formed. It is true that in the cases where this 
takes place within the ovary or the egg a definite form is assumed. 
But the same is the fact with the Foraminifera, the Radiolaria, 
the Fungi, and the other colonial organizations which arise exte- 
riorly through the continued subdivision of a germinal cell. 
There is no essential distinction between the two processes. The 
only visible distinction is that in the one case all this subdivision 
takes place exteriorly to the maternal body, in the other a greater 
or lesser portion of it takes place in a cavity of the maternal 
body which communicates with the external world, or within a 
capsular inclosure provided by the mother. 
The distinction, therefore, between Protozoa and Metazoa is by 
no means absolute, and the highest Metazoan is essentially a col- 
ony of Protozoa, since it is born asa single cell, and gains its 
mature form by a long series of asexual cell productions. Its 
main distinction is that many of these new cells are greatly spe- 
cialized, while in the simpler cell colonies they are to a great ex- 
tent generalized. 
The most primitive organic differentiation is into free cell and 
coherent cell individuals. Of the former there are numerous in- 
Stances in the Protozoan world, yet at a very low level of life 
asexually-born cells begin to cohere into colonies. From these, 
a a higher level, arises the only distinctive feature of the primi- 
tive Metazoan life, that of the formation of organized cell colo- 
nies within the maternal ovary or the egg, precedent to birth into 
the exterior world. However different this process may appear 
from the formation of the simpler cell colony, the difference is 
only in seeming, and the enclosed embryo perhaps very gradu- 
ally Succeeded to the external colony. ; 
‘hg first Significant step in this direction is taken at the low 
Of the Volvocinee. The globular colony of Volvox in fact 
acts as a sort of womb, into which are born asexual germs. These 
Der inito embryo colonies within the maternal body. We 
: re an instance closely analogous to that of Metazoan 
VOL ! 
XVI.—NO, 11, io 
