THE YOUNG INSECT 21 



diverse ways of feeding which the individual insect has 

 been able to adopt, in successive periods of its existence, 

 owing to the fact that it becomes winged after its final 

 moult. The habits of the more primitive insects, such 

 as the cockroach, are nearly the same throughout life. 

 Thus, external circumstances affect both the young and 

 the parent insect in a similar manner, and there is little 

 difference between the one and the other. But as we 

 follow the scale upward, we find that the adult insect 

 tends to become more and more unlike its immature form 

 in proportion as it makes use of its wings to explore new 

 territories, and to tap fresh sources of food-supply. More- 

 over, the change in the character of the food frequently 

 necessitates a profound modification of the mouth-parts — 

 as in the case of the biting caterpillar which ultimately 

 becomes a butterfly destined to suck sweet juices through 

 a trunk-like organ. A transformation so complete must 

 necessarily involve deep-seated physical processes: to 

 quote Lord Avebury, it " could hardly take place while 

 the insect was growing fast, and consequently feeding 

 voraciously ; nor, if the change could be thus effected, 

 would the mouth, in its intermediate stages, be in any 

 way fitted for biting and chewing leaves. The same 

 reasoning applies also to the digestive organs. Hence the 

 caterpillar undergoes little, if any, change, except in size, 

 and the metamorphosis is concentrated, so to say, into 

 the last two moults. The changes then become so rapid 

 and extensive that the intermediate period is necessarily 

 one of quiescence." 



We see, therefore, that the resting chrysalis or pupal 

 stage is an indispensable connecting link, among the higher 

 insects, between two totally distinct phases of life. Suc- 

 cessive steps in the evolution of metamorphosis may be 

 traced through the various groups, or orders, into which 



