152 METAMORPHOSES OP ANIMALS. 



391. If it be thus shown that the transformations which 

 take place in the embryo are of the same nature and of the 

 same importance as those which occur afterwards, the cir- 

 cumstance that some precede and others succeed birth, can- 

 not make any radical distinction between them. Both are 

 processes of the life of the individual. Now, as life does not 

 commence at birth, but goes still farther back, it is quite clear 

 that the modifications which supervene during the former 

 period are essentially the same as the later ones ; and, 

 hence, that metamorphoses, far from being an exception in 

 the Animal Kingdom, are one of its general features. 



392. We are therefore perfectly entitled to say that all 

 animals, without exception, undergo metamorphoses. Were 

 it not so, we should be at a loss to conceive why animals of 

 the same division present such wide differences ; and that 

 there should be, as in the class of Reptiles, some families 

 that undergo important metamorphoses, (the frogs, for ex- 

 ample), and others in which nothing of the kind is known, 

 (the Lizards and Tortoises). 



393. It is only by connecting the two kinds of transforma- 

 tion, namely, those which take place before, and those after 

 birth, that we are furnished with the means of ascertaining 

 the relative perfection of an animal ; in other words, 

 these transformations become, under such circumstances, a 

 natural key to the gradation of types. At the same time, 

 they will force upon us the conviction that there is an immu- 

 table principle presiding over all these changes, and regu- 

 lating them in a peculiar manner in each animal. 



394. These considerations are important, not only from 

 their bearing on classification, but not less so from the ap- 

 plication which may be made of them to the study of fossils. 

 If we examine attentively the fishes that have been found 

 in the different strata of the earth, we remark that those of 

 the most ancient deposits have in general preserved only the 



