6 



CHAPTER II. 

 OF THE STRUCTURE OF INSECTS IN GENERAL. 



IN Natural History, as in most other sciences, the 

 old adage, that there is no rule without an exception, 

 finds many applications, so that it is frequently dif- 

 ficult, or almost impossible, to give unexceptionable 

 characters for any particular group of animals. Thus 

 even the very short definition of an insect given in 

 the preceding chapter was not free from exceptions ; 

 but nevertheless, by far the greatest number of these 

 creatures present a very close resemblance in their 

 general structure ; and indeed the wonderful variety 

 which they apparently present, is produced entirely 

 by the modifications which the same elements undergo, 

 to fit these little creatures for the varied and important 

 parts assigned to them in the oeconomy of nature. 

 The object of the present Chapter is to give an account 

 of these general points of resemblance, with reference 

 only to such of their modifications as are necessary for 

 the proper understanding of the subject. 



External Skeleton. In most of the articulated ani- 

 mals, and especially in those provided with legs, the 

 segments of the body are formed of firm rings, united 

 with each other by a softer skin, by the aid of which 

 the hard case of the body acquires a greater or less 

 degree of flexibility. In some of these creatures, such 



