io 4 THE DARWINIAN THEORY 



no food, having indeed no mouth, but lives at the 

 expense of nutriment which it has accumulated in its 

 body during the caterpillar stage. After a time, 

 longer or shorter in different cases, the pupa skin is 

 cast off and the full-blown butterfly or moth appears ; 

 an animal altogether different to the caterpillar ; pro- 

 vided with two pairs of wings, with three pairs of 

 long jointed legs, with much more perfect sense- 

 organs, and with its jaws modified so as to form a 

 long tubular proboscis, by which it can suck up the 

 juices of flowers on which it now feeds. 



This is a typical case of abrupt metamorphosis, and 

 it is obvious that the developmental history cannot 

 here be a true recapitulation. It is quite impossible 

 that the pupa, for instance, should ever have been an 

 adult condition, and the abrupt character of the 

 changes from caterpillar to pupa, and from pupa to 

 imago, cannot be ancestral. Without entering at 

 length into the origin of metamorphoses such as 

 these, it may be pointed out that they only occur 

 amongst insects, in forms in which the nature of the 

 food, and therefore the structure of the jaws, is very 

 different in the caterpillar and in the adult condition 

 respectively ; and that in such cases a gradual 

 transition from one to the other would be quite im- 

 possible, for a mouth intermediate in its characters 

 between the masticatory mouth of the caterpillar and 

 the suctorial one of the butterfly would manifestly 

 be incapable of either biting leaves or sucking the 

 juices of flowers. 



In the case of other insects, such as the locust, 

 cricket, or grasshopper, the developmental history is 



