METAMORPHOSES OF ANIMALS. 151 



tration. The young White-fish, as we have seen (315), 

 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 vesicle. Much therefore 

 remains to be done, in order to complete its development. 

 But the fact of its being born does not prevent its future 

 evolution, which goes on without interruption. 



389. Similar inferences may be drawn from the develop- 

 ment of the chicken. The only difference is that the young 

 chicken is born in a more complete state, the most impor- 

 tant transformations having taken place during the embry- 

 onic period, while those to be undergone after birth are less 

 considerable, though they complete the process begun in the 

 embryo. Thus we 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. 



390. In certain Mammals, known under the name of 

 Marsupials (the Opossum and Kangaroo), the link between 

 the metamorphoses which take place before birth, and those 

 that occur 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 

 remain, each one fixed to a teat, until they are entirely de- 

 veloped. Even those animals which are born nearest to the 

 complete state have, nevertheless, transformations to un- 

 dergo. Ruminants acquire their horns ; and the lion his 

 mane. Most mammals, at birth, are destitute of teeth, and 

 incapable of using their limbs ; and all are dependent on 

 the mother and the milk secreted by her, until the stomach 

 is capable of digesting other aliment. 



