ANIMAL METAMORPHOSIS. 85 



law of nature, that the offspring of any animal shall, at birth, resem- 

 ble its parent in form and structure, needing only to increase in size 

 to assume all the parental characteristics. Nothing, however, can 

 be more erroneous than such a supposition. On the contrary, we 

 find that the large majority of the lower animals, at some period 

 of their existence, differ so vastly from their adult condition that 

 we can hardly conceive them to be the same creatures ; and 

 indeed, in many cases, the immature or larval forms have been 

 looked upon and described as distinct organisms until more care- 

 ful study has traced out their life-history, and proved them in 

 reality to be only transitional stages leading up to the mature 

 individual. 



Every creature in journeying through the successive phases of 

 its embryonic development assumes an immense variety of forms ; 

 but in the higher orders of the animal world, these changes are 

 concealed from the view of the ordinary observer, and occur 

 before the individual is capable of existing as an independent 

 being. No change can be more decided than the transformation 

 which a mammal undergoes at its birth ; when, owing to modifica- 

 tions of its respiratory and circulatory systems, it ceases to depend 

 for its nourishment on its parent, and becomes capable of enjoying 

 an independent existence. But this is not the change to which 

 the term metamorphosis is properly applied. Here the newly- 

 born animal at birth has all the parental features in miniature, and 

 has only to increase in size until it attains its full development. 

 The mode of performance of the principal functions is definitely 

 fixed, and though some of the organs may still be imperfectly 

 developed, yet all are there and none disappear. But in many 

 members of the animal kingdom important changes take place 

 after complete separation from the parent has occurred : modifica- 

 tion either of external form, or of some important organs directly 

 influencing the mode of life. We may find in the offspring some 

 complete apparatus undiscoverable in the parent ; or, on the other 

 hand, the parents may have organs which are entirely absent in 

 the offspring. 



Closely connected with metamorphosis, though differing from 

 it in the fact that one animal does not undergo the series of 

 changes in its own person, is what is called alternation of 



