360 METAMOEPHOSES OF ANIMALS. 



569. We have already shown that embryonic development 

 consists in a series of transformations ; the young animal en- 

 closed in the egg differing, at each period of its development, 

 from what it was before. But because these transformations 

 precede birth, and are therefore not generally observed, they 

 are not less important. To be satisfied that these transfor- 

 mations are in every respect similar to those which follow 

 birth, we have only to compare the changes which immedi- 

 ately precede birth with those which immediately follow it, 

 and we shall readily perceive that the latter are simply a con- 

 tinuation of the former, till all are completed. 



570. Let us recur to the development of fishes for illus- 

 tration. The young white-fish, as we have seen ( 471), is far 

 from having acquired its complete development, when born. 

 The vertical fins are not yet separate ; the mouth has not yet 

 its proper position ; the yolk has not yet retreated within the 

 cavity of the body, but hangs below the chest in the form of 

 a large bag. Much, therefore, remains to be changed, before 

 its development is complete. But the fact that it has been 

 born does not prevent its future evolution, which goes on 

 without interruption. 



571. Similar inferences maybe .drawn from the develop- 

 ment of the chick. The only difference is, that the young 

 chicken is born in a more mature state, the most important 

 transformations having taken place during the embryonic 

 period, while those to be undergone after birth are less con- 

 siderable, though they complete the process begun in the 

 embryo. Thuswe see it, shortly after birth, completely changing 

 its covering, and clothed with feathers instead of down ; still 

 later its crest appears, and its spurs begin to be developed. 



5/2. In certain mammals, known under the name of 

 marsupials (the opossum and kangaroo), the link between 

 the transformations which take place before birth, and those 

 occurring at a later period, is especially remarkable. These 

 animals are brought into the world so weak and undeveloped, 

 that they have to undergo a second gestation, in a pouch with 

 which the mother is furnished, and in which the young re- 

 main, each one fixed to a teat, until they are entirely developed. 

 Even those animals which are born nearest to the complete 

 states undergo, nevertheless, embryonic transformations. Ru- 

 minants acquire their horns ; and the lion his mane. Most 



