140 Conchology. 



completely formed previously to the developement of the animal; 

 and that it may be considered as an essential part of its organiza- 

 tion, let us now inquire into the mode by which its growth is ef- 

 fected. According to the decisive experiments of Reaumur, the 

 enlargements of shells is owing to a juxta-position, or successive 

 additions of earthy and animal matter, independent of any organ- 

 ized structure, Klein has supported a contrary opinion, and sup- 

 poses that the growth of shells is effected by intur-susception or a 

 kind of circulation. The opinion of Reaumur, however, has most 

 generally prevailed. Excepting Bonnet, few naturalists have 

 adopted that of Klein; and it will appear that this celebrated nat- 

 ui'alist was led to entertain concerning the mode of the formation 

 of shells, by the experiments of Herissant on the generation of 

 bone and shell. From these experiments it was clearly demon- 

 strated, that shells are composed of two substances, the one a 

 membranaceous or animal substance, and the other an earthy mat- 

 ter; but no such conclusion can be drawn from them in support 

 of the opinion, that the shell is a continuation of the body of the 

 animal; or that it is as closely connected as the bones in the bod- 

 ies of other animals; or even that this connection is formed by 

 means of fibres of the hgament which attaches the animal to its 

 shell; for it has been shown, that these muscular or ligamentous 

 fibres, in all descriptions of testaceous animals, are successively 

 separated, in proportion to the increase or enlargement of the 

 shell. This could not possibly take place, if the evolution and 

 formation of the shell, according to the opinion of Herissant, de- 

 pended on an internal circulation, analagous to what happens in 

 the body of the animal. In this case, the vessels which proceed 

 from its body, having no longer a communication with those which 

 are supposed to exist in the shell, it would be deprived of nourish- 

 ment, and consequently could not increase in size. And it is 

 found, that this separation takes place in all shells. It is gradual- 

 ly completed as the growth of the shell advances. 



A body may increase in volume in two different ways. Either 

 the particles of which it is composed pass through tliat body by 

 means of circulation, and undergo certain changes by which they 

 are prepared to form part of the body, or the particles of which a 

 body is composed, may unite with it by juxta-position, without 

 any previous circulation or preparation within the body, to the 

 increase of which they are destined. It is in the first way, that 

 the growth of vegetables and animals is accomplished; the second 

 is the mode by which shells receive new additions of matter, and 

 enlarge in size. The first is the mode of increase peculiar to liv- 

 ing, organized substances; by the second, inorganized substances 



