326 THE MECHANICAL FUNCTION'S. 



Nothing of this kind takes place among the Verte- 

 brata; where all the organs are developed in regular 

 and harmonious succession, without the slightest 

 mutual interference, and without those vicissitudes 

 of action and of torpidity, which we witness in the 

 chequered existence of the insect. 



§ 2. Structure and Composition of the 

 Osseous Fabric. 



The process employed for the formation and exten- 

 sion of the solid framework of the Vertebrata 

 differs totally from that which we have seen exem- 

 plified in the growth of shells, and of the hard 

 coverings of insects and crustaceous animals. These 

 latter structures, and the modes adopted for their 

 increase, are suited only to animals in which the 

 functions of the economy have not reached that 

 perfection to which they are carried in the higher 

 classes. In the more elaborate system of the ver- 

 tebrata, the skeleton is composed o^ ivne bones ; that 

 is, of solid pieces, which, although they are dense 

 calcareous structures, yet continue organized during 

 the whole period of developement, and form as 

 much a part of the living system as any other organ 

 of the body. We have formerly seen that the mem- 

 brane, in which the calcareous matter of the shell 

 is deposited, should properly be classed among the 

 integuments ; being analogous to them not only in 

 being situated externally, but also in their structure 

 and in their function. It is not so with bone, which 

 is essentially an internal structure.* 



* De Blainville regards the hard coverings of insects, together 

 with the shells of the Crustacea, as structures derived altogether from 



