LETTER XXXVI. 



EXTERNAL ANATOMY OF INSECTS 



CONTINUED. 

 THE ABDOMEN, AND ITS PARTS. 



The abdomen of insects, which we are next to consider, 

 is the third great section of the body, and is the seat of 

 the organs of generation, as well as of a principal part 

 of those connected with respiration. My remarks upon 

 it will be under the following heads : Its substance; ar- 

 ticulation with the trunk; composition; shape and pro- 

 portions; its appendages ; and its clothing. 



i. Substance. Under this head I may observe in ge- 

 neral, that where the abdomen is protected by hard elytra 

 or tegmina, as in most Coleoptera, and many Heteropte- 

 rous Hemiptera, the upper side is generally of a softer 

 and more flexible substance than the under, which from 

 its exposure requires a greater degree of hardness and 

 firmness to prevent its being injured. In some, — as the 

 Dynastidce and those beetles whose elytra are connate, 

 or as it were soldered together, the former is scarcely 

 more than membrane. In others of the above tribes, 

 nearly the whole of the back of whose abdomen, as in Sta- 

 phylinus; or only its anal extremity, as in Meloloniha ; or 

 its sides, as in Lygteus, &c, is not covered by the elytra 



