LAW OF ASSOCIATION IN THE ANIMAL KINGDOM. 
37 
The Coralliarian Polype is therefore constructed upon a very 
complicated type in comparison with the Hydroid Polype, and 
it is the latter type that we find realized yery clearly in the 
Stylasteridse. Their colonies present the polymorphism peculiar 
to the Hydroids. In them we constantly find nutritive indi- 
viduals, or gastrozooids, purveying individuals, or dactylozooids, 
and reproductive individuals, or gonozooids. In Spinipora, 
Sporadopora, Pliobothrius, and Errina , these different kinds of 
individuals are perfectly independent of each other ; a simple 
vascular network distributes among them the nourishment 
seized by the dactylozooids and elaborated by the nutritive 
individuals or gastrozooids. 
But in the Millepores the gastrozooid decidedly acquires 
the predominance. An important member of the colony, since 
it is this which prepares the nourishment for all, it attracts 
around it the dactylozooids and reproductive individuals ; all 
range themselves in a circle round the principal individual, 
but without entering into any intimate union with it. 
In Astylus , Sty taster, and Cryptohelia, this movement of 
concentration round the gastrozooid becomes still more strongly 
marked ; a vacant place is formed beneath it ; its tentacles, 
rendered useless by the vicinity of the dactylozooids, finally 
disappear ; it is reduced to a simple digestive sac, around which 
the dactylozooids perform functions exactly like those of the 
tentacles of a Coralliarian Polype. Here again, each system has 
very decidedly its own individuality, but with another step, the 
dactylozooids, still distinct throughout their length, become 
united at the base and attach themselves to the gastrozooid, 
and the gonozooids follow them in this movement. These 
different parts are thenceforward too close together to need a 
special vascular system to place them in communication ; the 
vessels which united them are no longer more than simple 
perforations of their wall, all opening into the vacant 
space situated beneath the gastrozooid, into which the gono- 
zooids themselves also penetrate ; but this whole, the most 
experienced naturalist would thenceforward be unable to dis- 
tinguish from what we call a Coralliarian Polype. 
The individual in the Coralliarian Polype is consequently an 
association of parts differing in form, each of which is equivalent 
to a Hydroid Polype. 
A Coralliarian Polype furnished with twelve tentacles, is the 
sum of a considerable number of Hydroid polypes, namely, a 
gastrozooid, twelve dactylozooids, and an indeterminate number 
of gonozooids. It is formed by means of the Hydroid polypes, 
like the flower by the agency of the leaves of the plant which 
bears it, or better still, like the composite flower by means of 
its florets. The phenomenon which has produced this polype 
