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spine, and which, as has been already mentioned, were of the palisadoe 
kind, the substance of which they were composed was found very much 
to resemble cork in its general appearance, and even in its structure, 
being so light and porous as not to allow them to sink in water. This, 
it will at once be seen, would be the kind of substance which would be 
particularly well calculated to perform those offices which we may pre- 
sume would belong to the supposed corresponding substance in the 
belemnite. Hence I feel little hesitation in concluding, that the spa- 
those part of the belemnite was originally a light pithy substance, by 
which the animal and its appendage were so poised in the water, as to 
be readily susceptible of those occasional changes in situation which 
the organization of the siphunculus seems to have been capable of 
producing. 
It is in favour of this opinion respecting the original structure of the 
belemnite, that on immersing a belemnite in a very weak mixture of 
muriatic acid and water, in the proportion of about twelve drops to a 
pint, several exceedingly delicate membranous Jlocculi became evident, 
hanging from the mass, and waving with the fluctuations of the fluid. 
The notion, then, which we seem to be authorized in forming, respecting 
the previous state of the belemnite, is, that it was a conical conca- 
merated shell, imbedded in a light porous body : a siphunculus passing 
through the septa, and perhaps terminating in the cellular part : the 
ascent or descent of the animal, with its dwelling, depending on the 
admission of air or of water into the siphunculus, and perhaps into the 
cellular part of the light body itself. This connection of the siphuncle 
with the light porous body is however assumed, on the existence of the 
tube passing through this body, as described by M. Walch, and which 
is discoverable in the specimen represented Plate VIII. Fig. 10. 
It is hardly necessary to observe, in favour of the marine origin of 
the belemnites, that they sometimes have other marine bodies, such as 
oysters, serpulee, &c. attached to their surface. This circumstance is, 
