' (50) 



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 by a developement of this kind, it may be compared to that which 

 forms the internal laminae of the hollow horns of the Ox, Sheep, and other 

 Ruminating Mammalia, and even to that by which the epidermis is produced 

 m all animals ; that is to 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 vertebrae. 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- 

 tinues to increase m 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 even provided v;\th 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, a A ter which they have no longer any occasion to change their 

 j m *. " llt ?Pl their skins they previously cast, though soft, are dead, and 

 already re r lacec [ j,y others, which develope themselves underneath that which 

 isdesti- iedtofalloff 



f> ..if the hard parts, therefore, of white blooded animals, whatever may be 

 aieir 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 blooded animals have also hard parts internally ; but they ai e 

 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 stomach 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 lamellae, 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 quincunx. 



As the superfices of the lamellae are plane, and those of the bone itself 

 convex, they necessarily intersect each other : the points of intersection are 

 marked on the surfaces of the bone by regular cuvilinear striae. These bones 

 have a kind of wings which are of a less opaque nature, less brittle, and have 

 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 

 loligoj bear a resemblance ; they are transparent, elastic, and very brittle; 



