LETTER XXXVI. 
EXTERNAL ANATOMY OF INSECTS 
CONTINUED. 
THE ABDOMEN AND ITS PARTS. 
Tue abdomen of insects, which we are next to consider, 
is the ¢hzrd 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 
ils exposure requires a greater degree of hardness and 
firmness to prevent its being injured. In some,—as the 
Dynastide 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 
Staphylinus ; or only its anal extremity, as in Melolontha ; 
or its s?des, as in Lygeus, Xc., is not covered by the 
