1890.] ENTOMOLOGICAL NEWS. IO3 



feet insect is divided into three regions, — the head, the thorax 

 and the abdomen. 



This division into regions is not to be confounded with the di- 

 vision into segments; each region consists of a number of seg- 

 ments. In the case of those insects undergoing a complete 

 transformation (butterflies, bees, beetles, etc.), it is only the 

 imago whose body shows clearly this division into three regions. 

 On the other hand, the larvae of such insects as dragonflies and 

 grasshoppers, whose transformation is incomplete, show a very 

 marked division into three regions, even when just hatched from 

 the egg. The tri-regional division of the body may be more or 

 less clearly perceived in those insects referred to in the first paper 

 as passing through two states, — fish moths and spring tails. 



Many of the segments of an insect^s body bear paired, jointed 

 appendages, one pair to a segment. These appendages may be 

 antennae (" feelers"), jaws, legs, claspers, etc. The wings, al- 

 though often spoken of as appendages, do not anatomically cor- 

 respond, or are not homologous^ to the appendages just referred to. 



The form, proportion, shape and relative development of the 

 difterent parts of the trunk and appendages of insects vary very 

 greatly. Only the more general, typical arrangement of these 

 parts will be described in these papers treating of insects in gen- 

 eral. The modifications must be left to subsequent papers on the 

 separate orders. In these general papers reference is usually 

 made to the imago, when describing anatomical parts. 



The Head of the imago is usually distinct from the rest of the 

 body. The segments of which it is composed are not easily dis- 

 tinguishable, owing to the sutures being more or less obliterated, 

 and one might be tempted to say at first sight, that it consisted 

 of but one segment. Comparative study, however, has shown 

 that it is composed, not of one, but of several segments. The 

 exact number is perhaps four, although this is not entirely certain. 



Prot. Comstock has adopted a convenient classification of the 

 parts of the head, which we cannot do better than follow here. 

 He divides the parts of the head into fixed parts and movable 

 parts. 



The fixed parts are the compound eyes, the simple eyes, the 

 occiput, the epicraniui?i, the clypeus, and the gnla. 



* In the technical language of Comparative Biology, homologous refers to anatomical 

 similarity, analogous \x> physiological similarity. 



