INSECT METAMORPHOSIS 



The degree of departure of the young from the parental 

 form varies much in different insects. In the cicada, for 

 example, the nymph is not essentially different in structure 

 from the adult except in the matter of the wings, the 

 organs of reproduction and egg laying, and the musical 



Fig. 132. The life history of a ladybeetle, Adalia bipunclata 



A, the adult beetle. B, group of eggs on under surface of a leaf. C, a young 



larval beetle covered with white wax. D, the full-grown larva. E, the pupa 



attached to a leaf by the discarded larval skin 



instrument. But the habitats of the two forms are widely 

 separated, and it is unquestionable that, in the case of the 

 cicada, it is the nymph that has made the innovation in 

 adopting an underground life, for with most of the rela- 

 tives of the cicada the young live practically the same life 

 as the adults. 



Animals live for business, not for pleasure; and all their 

 instincts and their useful structures are developed for 

 practical purposes. Therefore, where the young and the 

 adult of any species differ in form or structure, we may be 

 sure that each is modified for some particular purpose of 

 its own. The two principal functions of any animal are 

 the obtaining of food for its own sustenance, and the 



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