110 Odier on the Chemical composition 



comparing these results with those obtained by M. Chevreul in his 

 experiments on the cruslacea, we see the difference between the 

 composition of the salts of the carapace of those animals, and that 

 of the salts of the same organs in insects. 



The presence of sub-carbonate is a very remarkable character in 

 the latter, and is not found in the former. Phosphate of lime, which 

 exists in small quantity only in the Crustacea, forms the greater 

 part of the salts contained in the coverings of insects. The absence 

 of carbonate of lime in these, whilst it forms the base of the cara- 

 pace of the former, is another great point of difference : phosphate 

 of iron is here found accompanying the phosphate of lime, as it is 

 in almost all the parts of animals in which the latter is deposited. 

 It is very probable that a little phosphate of magnesia may form 

 part of the salts of the hard parts of insects, but the small quantity 

 of matter on which I operated did not allow me to seek for it ; I 

 grounded my supposition, however, on the obserTation of M. 

 Robiquet, who found phosphate of magnesia in cantharides, which 

 he supposed to have been derive^^ from the skeletons of those 

 animals. 



The difference that exists between insects and Crustacea, as to. 

 the nature of the salts of their hard parts, proves very palpably the 

 error which some naturalists have fallen into, who have attempted 

 to establish analogies of organization on the chemical nature of 

 those organs. According to their views, we should expect to find 

 nearly the same materials in insects, as in the Crustacea to which 

 they are so nearly allied, and yet we observe the most decided 

 <lifference. What becomes of the law which a distinguished natu- 

 ralist thinks he has observed, according to whom the superior ani- 

 mals are characterized by their bones being formed of most phos- 

 phate of lime, and a smaller proportion of carbonate, and the 

 inferior, by having a large proportion of carbonate and a small 

 quantity only of calcareous phosphate in their composition ? On- 

 this view insects must quit the place assigned them by Nature, and 

 be associated with animals of the first order, to which, however, 

 no naturalist has pretended to ally them. 



If the results I have obtained do not coincide with the ideas ©f 

 some naturalists, they will not, I believe, by any means astonish 



