184 METAMORPHOSES OF 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 mark 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, and continuous with, the 

 later ones ; and hence, that metamorphoses, far from being 

 exceptional in the case of Insects, are one of the general 

 features of the Animal Kingdom. 



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 observed 

 after birth, (the Lizards and Tortoises.) 



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

 tions, 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 immutable prin- 

 ciple presiding over all these changes, and regulating them 

 in a peculiar manner in each animal. 



394. These considerations are exceedingly important, not 

 only from their bearing upon classification, but not less so from 

 the application 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 



