40 
rOPULAR SCIENCE REVIEW. 
together without exposing them to death, the different parts of 
a highly individualized society die without being able to recon- 
struct themselves ; the reproductive function is thus exclusively 
reduced to its sexual form. 
The Sponges reveal to us their colonial nature even more 
distinctly than the Hydraids. In them, in fact, the Spongiarian 
individual is certainly constituted by two kinds of cellular indi- 
viduals , the Amoeba and the flagellate Infusory, the analogues 
of which are to be met with at liberty in the state of isolated 
individuals. The flagelliferous cells of Sponges present quite 
exceptional peculiarities ; they are furnished with a nucleus, and 
a contractile vesicle, and their flagellum is surrounded by a 
membranous collar in the form of a funnel. All these characters 
are to be met with in the Codosigce* which are unicellular Infusoria 
that always live isolated, and which in consequence are to the 
Sponges what the Hydras are to the Siphonophora and Coral- 
liaria. In the A nthophy see these cells always live in colonies, but 
they are still all alike. Let polymorphism step in, — let some 
of the associated cells retain the flagelliferous form, whilst 
others become Amoebae (a transformation which is quite possible, 
since it is one of the most frequent modes of reproduction of the 
amoeboid Infusoria), and the Anthophysa is transformed into a 
sponge. Thus the process is always the same ; whatever may 
be the materials which Nature brings together, cells or polypes, 
she subjects them all to the same elaboration in order to obtain 
from them new individuals. 
The cells, when once brought together, maj^ moreover, within 
the organisms containing them, undergo in a high degree 
those metamorphoses which are the consequence of the physio- 
logical division of labour, and form diverse organs, although 
these organs cannot be regarded as actual individuals. If 
the individuals of a colony often descend to the state of organs, 
we must not conclude from this that the organs of an animal 
are always individuals which have lost their autonomy ; but 
the animal to which they belong, although it may never have 
been an assemblage of individualities intermediate between its 
own and that of the cells, is none the less a colony of the 
latter, subjected to the laws of evolution of all the others. 
Thus, even if it should be proved that the Vertebrata and 
the Mollusca are not the result of the fusion of simpler organ- 
isms which have once been able to lead an independent life, they 
would be none the less colonies of cells, and the law of association 
would lose none of its generality. 
It remains the fundamental law of the development of the 
See an article by Mr. W. Savile Kent, in Popular Science Review, N. S., 
Vol. II., p. 1 13, with illustrations. 
