LAW OF ASSOCIATION IN THE ANIMAL KINGDOM. o9 
formed into an Arachnid or an Insect, how the various 
Crustacea have issued from a common stem, and how, from 
another form of colony, the Annelidan series may have pro- 
ceeded. 
On the other hand, it has been repeatedly maintained that 
the Sea-urchins, the Starfishes, and the Ophiurans, were 
nothing hut colonies of worms soldered together by the head ; 
they are certainly colonies, but of a very peculiar nature. 
Can we say the same of the Mollusca and Yertebrata, all 
the parts of which seem to us to be so intimately fused together, 
and which are the giants of creation P Are there simple forms 
the association of which could explain to us the marvellous 
organization of these superior types, as we have explained the 
formation of the Siphonophora, the Coral liaria, the Echino- 
dermata, the Yermes, and the ArthropodaP This is what we 
have still to investigate, but it is important to remark, that 
whatever may be the result arrived at, the generality of the 
principle of association will not be at all invalidated. If, in 
opposition to the presentiments derived from our previous 
studies, these simple individualities never existed, we should 
have in fact to compare the Mollusca and the Yertebrata with 
the primordial individuals, the combinations of which have 
produced the other types, and which we may still recognize as 
the base of all the great groups of the animal kingdom. Now, 
how did these individuals themselves originate ? 
The Ilydrse and other analogous organisms furnish our 
answer. We may cut a Hydra into as many pieces as we like, 
each of these pieces, far from dying, continues to develope 
itself, and, finally, reconstructs the perfect Hydra. What are 
we to conclude from this, if not that the different parts are 
independent of each other, as the polypes forming one of the 
lowest colonies are of their neighbours? Each cell of the 
Hydra is an actual individual, and the Hydra is a colony of 
these unicellular organisms, just as the Siphonophora are them- 
selves colonies of Hydras. The aptitude for social life is 
communicated by heredity to these cells as to the polypes. 
Each cell, and each polype, when detached from a colony, 
bears within it, as it were, the effigies of the colony, and its 
subsequent development tends always to the reconstruction of 
the latter. At first, all the members of a colony are equally 
apt to reproduce it ; thus this faculty, like the others, becomes 
localized and tends to become the appanage of certain individuals 
or of certain parts ; at the same time sexual reproduction 
gradually increases in importance ; and when the society has 
attained a certain degree of coherence its different parts cease 
to be able to live independently of each other. As in the case 
of old people who cannot be separated after a long existence 
