48 INTRODUCTION. 



parent's body; the moment it is thence detached, 

 it receives a distinct life of its own, resembling 

 that of the parent in most of its essential elements. 



But the germ, the embryo, the foetus, and the 

 new born animal, never possess the perfect form of 

 the adult, and sometimes the difference is so con- 

 siderable, as to permit us to give the final change to 

 their perfect form the name of a metamorphosis. 

 Thus, for example, it would be impossible, unless 

 we were aware of the fact from previous observation 

 or information, to divine or conceive, that a cater- 

 pillar could ever become a butterfly. 



All living beings are more or less metamorphosed 

 in the progress of their growth to maturity; cer- 

 tain parts are lost, and others more completely de- 

 veloped in the course of their advancement. The 

 antennaB, the wings, all the parts of the butterfly, 

 were enclosed within the skin of the caterpillar; 

 with that skin disappear the jaws, the feet, and 

 other organs which belong not to the butterfly. The 

 feet of the frog lie concealed under the covering of 

 the tadpole, and when the latter becomes a frog it 

 loses the tail, the mouth, and the gills. The in- 

 fant at its birth loses the placenta and the caul; 

 at a certain age it loses almost entirely the tymns, 

 and gains, by degrees, hair, teeth, and beard ; the 

 body augments more than the head, the head more 



than the internal part of the ear, $*c. 



