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 after- 

 wards, the circumstance that some precede and others 

 succeed birth cannot mark any radical distinction be- 

 tween them. Both are processes of the life of the indi- 

 vidual. Now, as life does not commence at birth, but 

 goes still farther back, it is quite clear that the modifi- 

 cations which supervene during the former period are 

 essentially the same as, and continuous with, the latei 

 ones ; and hence, that metamorphoses, far from being 

 exceptional i# the case of Insects, are one of the gen- 

 eral 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 differ- 

 ences ; and that there should be, as in the class of Rep- 

 tiles, some families that undergo important metamor- 

 phoses, (the frogs, for example,) 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 trans- 

 formations, 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 tne convic- 

 tion that there is an immutable principle presiding over 

 all these changes, and regulating them in a peculiar 

 manner in each animal. 



394. These considerations are exceedingly impor- 

 tant, 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 exam- 

 ine attentively the fishes that have been found in 

 the different strata of the earth, we remark that 



