32 
POPULAR SCIENCE REVIEW. 
peculiar corporation, incessantly in action, is the ordinary 
medium of these exchanges ; the blood globules are true traders, 
conveying with them in the liquid in which they float, the 
multifarious merchandize in which they deal. 
All the comparisons that could be furnished by the degrees 
of relationship were employed to express the affinities presented 
by animals even before it was supposed that any real con- 
sanguinity existed between them ; and just in the same way 
the organisms themselves have always been compared to 
societies, or societies to organisms, without any recognition 
that these comparisons were otherwise than purely ideal. On 
the other hand, we arrived last year at the conclusion that 
association had played an important if not an exclusive part in the 
gradual development of organisms ; we find absolutely convinc- 
ing proofs of this in the history of Polypes, and of the Yermes ; 
the affinities of the latter to the Arthropods are doubted by no 
one ; and we have shown how these same Yermes are connected 
with the Mollusca and the Yertebrata. The theory therefore 
extends to the whole animal kingdom. 
But, in the first place, what are we to understand by asso- 
ciation ? In saying that animal organisms have been chiefly 
produced by the transformation of animal societies into in- 
dividuals, what are we to understand by the term societies ? 
Are we to say that every society of living creatures may be an 
individual in course of formation P Certainly not ; but there 
are animal societies, in which the relations of the individuals 
are so close that each individual is not only in immediate 
contact, but also in histological continuity with its neighbours. 
To such a society we give the name of colony, which some 
naturalists have changed to cormus. The individuals composing 
these colonies, or cormi, are not always indissolubly united to 
each other. They may separate from their companions, live 
isolated for a longer or shorter time, and even form new 
colonies, thus indisputably asserting their independence. In 
the same zoological group we may find allied species, in some 
of which the individuals live always solitary, while in the 
others they are on the contrary always associated. This is the 
case in the very remarkable group of the Polypes or 
Acalephs. 
One species of this group — the brown Hydra {Hydra fasca ) — 
is common in our stagnant waters, and even in very small garden 
basins. It has never ceased to excite the interest of naturalists 
and philosophers since Trembley first made known its marvellous 
faculties. These Hydras usually live solitary, but frequently 
the larger individuals may be seen bearing smaller ones upon 
the wall of their body. In a Hydra kept in confinement the 
development of these may be followed step by step. They are 
