GROWTH AND TRANSFORMATION i6i 



the old cuticle may slip off backwards and in some cases be 

 turned partly inside out. The cuticular linings of the fore- 

 gut, hind-gut, and air-tubes are shed along with the exo- 

 skeleton. After emergence the parts of the creature's body 

 in its new form have room to expand ; the sclerites of the 

 cuticle become firm and darkened so as to assume their 

 characteristic colour, and the successive layers of secondary 

 cuticle begin to form on the surface of the skin beneath the 

 first-formed or primary cuticle. When no longer confined 

 in its " old husk " the insect undergoes a process of expansion 

 through the smoothing out of the folds and wrinkles in the 

 body- wall, so that while it often assumes a form like that 

 which it had borne in the previous stage of its life, it shows 

 soon after the moult a considerable increase in size. Thus 

 through its series of castings and renewals of the cuticle it 

 may grow to a bulk many times greater than it possessed at 

 hatching. Growth accompanied by a number of moults is 

 a necessary feature in the life after hatching of the great 

 majority of insects, and they share this feature with members 

 of other classes of the great group of Arthropoda. 



But most insects, when adult, are strikingly distinguished 

 from other arthropods by the possession of wings and the 

 power of flight ; the wings furnish a most distinctive and 

 characteristic feature in the insect's structure. Now, while 

 many insects, such as cockroaches, grasshoppers, and 

 plant-bugs, are hatched in a form generally resembling their 

 parents, displaying the same general build of body, shape, 

 and proportions of legs, nature and function of jaws, there 

 is no trace of wings to be seen on these newly hatched 

 young. Every one knows that such a familiar insect-larva 

 as a butterfly's caterpillar exhibits no trace of wings, and the 

 same condition is noticeable in all insects newly hatched or 

 born. So we see that while insects, like arthropods gene- 

 rally, pass through a series of moults in the course of their 

 growth, the development of the wings that are distinctive 

 of the vast majority of insects is carried on during this post- 

 embryonic period, and that no insect has its wings already 

 formed when it first appears in the outside world. 



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