118 METAMOKPHOSES OF MAN 



these functions. We stated, also, that as a conse- 

 quence of this pro vision, birds and lizards are completely- 

 organized within the isolated egg, whilst, on the con- 

 trary, mammals are forced, in order to reach the same 

 condition of development, to remain within the 

 mother's uterus, where they are nourished through 

 the medium of truly temporary organs. Now, as (for 

 a reason which doubtless we shall never be acquainted 

 with) an egg with a small vitellus may be destined to 

 be expelled, there is, nevertheless, a necessity for a 

 mode of existence during the state intermediate be- 

 tween the embryonic and fully-formed animal; and 

 this necessity must be provided for. 



This is one of those problems which Nature sets for 

 herself, as it were, for the mere pleasure of solving 

 them — the solution in this instance being found in 

 the phenomenon of metamorphoses. We invariably 

 find, even among species which undergo recurrent 

 metamorphoses, that the embryo which springs from 

 the egg presents a relatively more simple organiza- 

 tion than the adult ; hence its wants are fewer, and it 

 can satisfy them. Gradually it becomes fully formed, 

 its sphere of activity is enlarged, and finally it assumes 

 its adult characters when it has received the requisite 

 materials from the external world. 



The larva, then, is but an embryo leading an inde- 

 pendent life, which feeds itself instead of being 

 nourished by the mother, and which undergoes, 

 externally, beneath our very eyes, changes — trans- 

 formations — which take place, among vivipara, in the 

 depth of the mother's uterus.* In assigning the 



* I give, word for word, the substance of an article which may 

 be considered as the first edition of this chapter (1855). M. Cla- 



