SEGMENTS OF THE BODY, 22/ 



By Linnaeus, the body of an insect was divided into four 

 parts : the head, trunk, abdomen, and Umbs. The latter, 

 however, more properly belong to the second of these divi- 

 sions, of which they are appendages ; and the term thorax is 

 now generally apphed to designate the Linnaan trunk. 

 Hence I have now to treat upon the head, thorax, and 

 abdomen. These three divisions, as respectively comprising 

 the principal organs of sensation, locomotion, and genera- 

 tion, appear to be completely in unison with nature, and 

 have accordingly been universally adopted and employed. 

 That persons ignorant of the comparative anatomy of insects 

 should have blundered in their trivial descriptions of insects, 

 and miscalled any of these parts, can be no argument against 

 their correctness; neither can it be sufficient ground for 

 asserting (as has recently been done) that " their wings are 

 either thoracical or abdominal appendages, as an entomo- 

 logist pleases," and that, therefore, there are no such parts 

 in an insect as a thorax or an abdomen, which names should 

 consequently be rejected in favour of a series of names for 

 each iudi\ddual segment. 



But, in addition to these three primary divisions, the body 

 of insects consists of a series of secondary di^^sions, or rings, 

 of which the head exhibits no distinct trace. The thorax, 

 on the contrary, is always divisible into three segments; 

 and the abdomen is in general variable in the numbers of 

 its segments, from six to nine, exclusive of the organs of 

 generation. On comparing the different segments of a per- 

 fect insect, various striking differences will be observed, 

 depending principally upon the presence or absence of the 

 appendages, or organs, which these segments respectively 

 sui)port, as well as upon the degree of their develop ement. 

 Thus, when one of these segments has attained its greatest 

 extent and complication, and the appendages which it sup- 

 ports have reached their maximum, it is perceived that the 



