C 807 ] 
folitude. The fame difpofitions we find imprefled on 
thofe of the aquatic fyftem : then why not among 
the polypi ? as is evidently feen from the prodigious 
variety of coral bodies, where it feems in fome as if 
thouiands ailed in concert together ; in others, where 
each ails for itfelf ; of which latter is the belemnites. 
The fihape of the belemnites is generally more or 
lefs conic, terminating in a point, and of various co- 
lours, according to the juices of the ftratum in which 
it lay : it has ufually a feam or fiflure, running down 
the whole length of it, fometimes filled with a creta- 
ceous fubftance. In fome it is in the middle or axis 
of the body; in others on one fide. Its interior con- 
flitution feems compofed of feveral conoid cortices, 
or crufts, which, when broken tranfverfely, appear to 
proceed in ftriae or rays from the feam or centre ; 
which feam I take to have been the habitation or cell 
of the animal in its polyp ftate, and in which the 
body was affixed ; or perhaps ferving as a fyphuncu- 
lus, in which was a ligament that proceeded from 
the nucleus in its perfedl ftate. 
The crufts that it is compofed of, I fhould appre- 
hend, denote certain periods in the age of the animal; 
as the annual rings in a piece of timber, its age : but 
what thofe periods are, we are unacquainted with ; 
fee Fig. 7, 8, 9, and 1 1. 
The animals of the teftaceous tribe in general, as 
they increafe in age, increafe their fhell in thicknefs, 
until they have lived their ftated time, or attained to 
good old age ; and that is done by adding a new cruft 
or lamina to it, as feveral, if not all the tubuli, the 
oyfters, and the nautili, witnefs (but thefe obferva- 
tions are beft made on foffil bodies, when, by great 
length 
