32 ROMANCE OF THE INSECT WORLD CHAP. 



and not violent and great. But leaving these cases 

 out of the question, the fact remains that an insect's 

 life is generally apparently devisable into four well- 

 marked states, and the change from the one to 

 the other appears to be quite abrupt. In reality the 

 metamorphoses of insects, like those of all other 

 animals, arc continuous. The whole alteration, from 

 the egg to the caterpillar, to the pupa, and from this 

 to the perfect insect, proceeds gradually, and the 

 striking changes in outward form, which take place 

 from time to time and very rapidly, are simply due to 

 a throwing off of the outer skin revealing a creature 

 which, far from being new, has been in preparation 

 for days ; sometimes for months. 1 



The skin of an insect is very different from our own 

 and from that of other vertebrate animals. It serves 

 in place of a bony skeleton, and is more or less hard 

 because to it the muscles are attached. When it is 

 once made it cannot be altered, and consequently 

 no change of form is possible without a cast of 

 skin. In the case of many larvae the moultings 

 are necessitated principally by growth and increase in 

 size ; the alterations of structure are confined to the 

 two last and more important skin-sheddings. Thus, 

 then, the apparent abruptness of the changes of 

 insects is to be attributed, in great measure, to the 

 peculiar nature of their skin. 



That material change of form is often delayed 



until towards the latter end of development, or 



until the period of pupa, may be accounted for 



partly by the structure of the mouth. That of the 



1 Sir John Lubbock. 



