OBSERVATIONS ON THE ANIMALS, &c. 453 
correction and explanation are required, to allow for the alteration 
produced by a long entombment in a more or less calcareous stra- 
tum. There are few instances, perhaps, where this kind of inquiry 
is more wanted, than the one before us. In the first place, the 
structure of the solid part is fibro-calcareous, and its weight consi- 
derable ; but if this now stony mass be exposed to great heat, a 
strong smell is emitted, resembling that of burning horn, just as 
would happen if a frame-work of horny membrane—cellular as all 
organized matter is—had been petrified by the infiltration of carbe- 
nate of lime, which, we know, would fill up the empty space, and, 
providing the structure were originally fibrous and radiating from 
an axis, would present precisely the appearance which the fossil Be- 
lemnite does present. It is so highly improbable, and contrary to 
all analogy, that the hard parts of a highly organized animal should 
consist of a thick, heavy, stony cylinder, of considerably greater spe- 
cific gravity than the fluid in which it lived, and so clear from 
actual observation that horny matter did enter into the composition 
of this curious organ, that there can be little doubt of its having 
been, when forming part of an animal, a light horny skeleton, and 
converted afterwards, and by a slow process, into its present petri- 
fied condition. 
But, secondly, the contents of the aperture are by no means to be 
taken as the real substance which once was included in the body of 
the animal. The series of plates we have alluded to merely serves 
to give us an idea of the shape of the once empty chambers, whose 
septa, or walls of separation, filled the space between them. This 
conical interior (called the alveolus) is, in fact, all that remains of the 
chambered portion of the shell, and resembles an Orthoceratite in 
its general appearance. It is not unlike that fossil in structure and 
use, as well as in external configuration. 
Again: we have said above that the Belemnite sometimes bulges 
out towards the larger extremity ; but this description gives a very 
faint idea of the nature of the aperture and parts connected with it, 
from which, indeed, the most interesting and instructive facts are 
learnt. Commencing at the base of the hollow cone of the sheath 
—as the fibro-calcareous part is called—there is now known to have 
extended a horny cup, in which great part of the viscera, &c. of the 
animal, were included ; and besides these a quantity of black fluid, 
capable of being spirted out, at a moment of danger, to darken the 
water, and give time to the animal to escape from its enemies. 
We can now understand the more correct and complete definition 
of a Belemnite, namely, that it was made up of three parts—a skele- 
