286 Dr. Mac Culloch on the 
produce a common structure, is managed, we cannot conjec- 
ture: but it might be imagined, did we not know the inde- ° 
pendent and single vorticella, that the ramous one was itself 
but one animal, and that the flowers, or single vorticelle, were 
only its parts. The whole dependence presents a singular 
analogy to the vegetable identity, where all the leaves and 
flowers conspire together to produce and propagate the plant ; 
so as almost to lead us to conclude that there was here a per- 
fect gradation from one department of nature to the other. 
This explains the dependence of the coral colony, as far as 
one difficulty can explain another. The only difference consists 
in the hardness or softness of the habitation, or tree, if it may 
be so called. In the voréicella it is a soft animal matter; in 
the coral it is bony, or stony. And here also even the corals 
present an analogy to those vegetables which, like the chara 
and the coralline, incrust themselves with calcareous earth, or 
to the equisetum, which secretes a siliceous bark. 
To take the inhabitant of the madrepore as an example of the 
animal itself, it may be considered as formed of the shell, the 
head, a centre, and the feet or hands: the latter are very 
numerous, and are divided or split at the extremities, while 
they surround the body of the animal in the form of a circle. 
Each of these feet or hands embraces a lamella of the star of the 
madrepore, so that they serve both for the construction of the 
shell, and for fixing the animal in it. The pedicle, or single 
part of the hand, appears to be of a muscular nature, and is 
fixed in a cylindrical tube, which is properly the body of the 
animal. Within this is a stellated body, which is supposed to 
be the head, quick in its motions; while the rays seems to be 
the tentacula by which it feeds itself. 
The different species of corals engaged in the formation of 
the coral banks are not all known; but some of the genera, at 
least, and a few of the species, have been ascertained. The 
chief of these are madrepore of different kinds; millepore, 
among which the cerulea has been discovered; the tubipora 
musica; a caryophyllia, a distichopora, and a corallina. 
Astreee, echini, and other animals, living and dying on the 
