Larva and Imago 125 



vanishes quickly away. They furnish an extreme 

 illustration of that "division of labour" between the 

 larval and perfect stages to be observed, more or 

 less, in all insects which undergo a metamorphosis. 

 An animal has both to feed that it may live its own 

 life, and to leave behind it offspring to continue the 

 life of the race. Among insects these two functions 

 — feeding and reproduction — tend to become divided 

 between the stages of the life-history. The great 

 business of a larva is to take in food so as to store up 

 a supply of material whence the parts of the imago can 

 be built up -, its organs of generation being unde- 

 veloped it is incapable of propagating the race. But 

 the principal function of the perfect insect is not 

 feeding but breeding. The ovaries of the female are 

 often so large that the hind-body seems full of eggs. 

 The male is provided with elaborate sense-organs, 

 enabling him to discover the female, often also with 

 scent- and sound-producing structures to allure her 

 when discovered. Everything is adapted to secure a 

 speedy pairing of the sexes. After the egg-laying, 

 the parents, their work being done, may as well die, 

 except in those cases where their exertions are needed 

 to get food for the young. The life of the perfect 

 insect thus tends to be shortened, and even in cases 

 where feeding goes on, the duration of the imaginal 

 state is very brief as compared with the life of the 

 larva. A grub feeds industriously underground for 

 years that a Chafer may live for a few weeks in the 

 upper air. And in the most extreme cases — the May- 

 flies and the Silkworm-moth for example — the jaws 

 are so greatly reduced that feeding by the imago is 

 impossible, and the division of labour between the 

 stages is perfected ; feeding is entirely confined to 

 the larva, and the perfect insects have but to pair 

 speedily, lay their eggs, and die. 



