CHAPTER II 



FORM, GROWTH, AND CHANGE 



IT may seem paradoxical to begin the study of develop- 

 ment among insects with the examination of a fully- 

 grown specimen of the group, but it is towards this 

 adult condition that development tends. The caterpillar may 

 be regarded from one view-point at least, as the preparation 

 for the butterfly ; and the structure and habits of the immature 

 creature can be satisfactorily explained only in the light of 

 what is to be the end of its life-story. 



It is common knowledge that in most groups of animals, the 

 naturalist can distinguish more or less easily between " lower " 

 or more generalized and " higher ' or more specialized 

 members. The organs of a creature of the latter grade can 

 be understood only by comparing them with the corresponding 

 parts in a more lowly relation, and it is now generally 

 believed that specialization of any kind of living creatures has 

 been attained by progressive changes from simple beginnings, 

 not only in the life-story of the individual but also in the history 

 of the race. Therefore, in a study of insect structure, it is 

 inadvisable to begin with so highly organized and specialized 

 a creature as a butterfly, a bee, or a blue-bottle. Some more 

 simply-built insect will be more suitable, though we may indeed 

 find that the most simple furnish us with details sufficient for 

 years of research. We can profitably start with an insect 

 like that first mentioned on the first page of this book 

 a grasshopper or locust (Fig. i) which belongs to a 

 comparatively lowly order, and shows, as already men- 

 tioned, no striking difference between the young and the 

 adult. 



The outer covering of the body is for the most part hard and 

 firm ; it may fairly be described as horny. Such a firm cuticle 

 characterises generally all members of the Arthropoda, a great 



