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at certain periods, cast their old shells entirely off, and acquire new ones ; 
but this re-production may also take place by development, as in the horns 
of the Deer. If the internal strata of those shells which are not cast off, be 
produced bya developement of this kind, it may be compared to that which 
forms the internal laminz of the hollow horns of the Ox, Sheep, and other 
Ruminating Mammalia, and even to that by which the epidermis is produced 
in all animals; that isto say, there must take place a withering, or, as it were, 
the death of a membrane, which seems to preserve a sort of organization 
while it remains unexposed to external elements, or while it has not acquired 
its proper degree of solidity. 
In this manner, it appears, are produced all the hard parts which may be 
regarded as the bones of animals that have no vertebre. In cray-fish, for 
example, the calcareous crust which, in them, is at once skin and skeleton, 
grows no more after it is completely indurated. The animal, however, con- 
linues to increase in all its soft parts; and when these become too much 
confined by the envelope, the latter splits and is detached : but a new covering 
is found below the old one, which is formed while the latter loses its con- 
nection with the body, and as it were dies. The new envelope is at first soft, 
sensible, and eyen provided with vessels : but a quantity of calcareous par- 
ticles, previously accumulated in the stomach, is soon deposited in this 
covering, hardens it, obstructs the pores and the vessels, and renders it in 
every respect similar to the shell it has replaced. 
The induration of the covering of insects is not completed until they acquire 
their last form, after which they have no longer any occasion to change their 
skin: but all their skins they previously cast, though soft, are dead, and 
already replaced by others, which develope themselves underneath that which 
is destined to fall off. 
All the hard parts, therefore, of white blooded animals, whatever may be 
their consistence and chemical nature, ought to be compared with respect to 
the manner of their growth to the epidermis, to nails, and to hollow horns, 
rather than to real bones. 'The same remark should perhaps be applied to 
certain external parts of fishes, though their substance is strictly osseous; for 
instance, to the bucklers of the Sturgeon and Cyclopterus, and the spinous 
tubercles of the Ray. 
Some white losticd animals have also hard parts internally; but they are 
not articulated in such a manner as to form the bases of moveable members, 
and their texture differs considerably from that of ordinary bones. The most 
remarkable of these hard parts are the teeth in the donee of the lobster. 
The common Cuttle-fish (Sepia officinalis) contains in the flesh of the 
back an oval substance, convex before and behind, white, solid, friable, and 
of a calcareous nature. This substance is not attached to the flesh, but has 
the appearance of a foreign body introduced into it. 'There is no indication 
of any vessel or nerve penetrating it, nor is any tendon affixed to it. It is 
composed of thin parallel lamelke, which are not in immediate contact with 
each other. ‘The intervals are occupied by an infinite number of small 
hollow columns standing perpendicular between one lamella and another, and 
arranged in a very regular guincunx. 
As the superfices of the lamelle are plane, and those of the bone itself 
convex, they necessarily mtersect each other: the points of intersection are 
marked on the surfaces of the bone by regular cuvilinear striz. ‘lhese bones 
have a kind of wings which are of a less opaque nature, less brittle, and haye 
greater resemblance to thin elastic horn. than the body of the bone. 
To this last substance the parts called the bone in the Calmar (Sepia 
loligo) bear a resemblance; they are transparent, elastic, and yery brittle ; 
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