I METAMORPHOSES OF INSECTS 33 



caterpillar is provided with jaws, fitted for eating 

 leaves, whereas the mouth of the butterfly is suctorial, 

 and capable only of sucking the nectar from flowers. 

 It is clear that were the mouth of the larva meta- 

 morphosed into that of the perfect insect by a series 

 of small changes, the insect in the meanwhile would 

 be unable to feed, and must die of starvation in the 

 midst of plenty. In insects like the locust, whose 

 changes are gradual, the mouth of the so-called larva 

 resembles that of the perfect form. 



No doubt to this change in the mouth-parts, and to 

 the similarly rapid and extensive alterations going 

 on in the pupa, is to be attributed the strange, and 

 otherwise incomprehensible, immobility of this re- 

 markable period. Not only, as in that of a butter- 

 fly, the mouth is in a state of transition, the digestive 

 organs and the important muscles, and even the 

 nervous system, are in course of rapid change. It 

 must not be forgotten that all insects are inactive for 

 a longer or shorter time after each moult. The period 

 of inaction varies, being short as a rule when the 

 change is slight, and becomes correspondingly pro- 

 longed as the change increases in magnitude. The 

 quiescence of the pupa is therefore not a condition 

 peculiar to this stage, but an exaggeration of the rest 

 that has succeeded every previous change of skin. 1 



1 Sir John Lubbock. 



D 



