290 PTILOTA : IMAGO — EXTERNAL ANATOMY. 



the back {dorsum), and the ventral ones the belly {venter). 

 We have already seen that, in the larva state, several seg- 

 ments exist which are not found in the imago ; and the exa- 

 mination of the abdomen in various insects clearly proves, that 

 these last segments are abdominal ones. Thus, if a male 

 earwig be examined, it will be perceived that there are nine 

 distinct abdominal segments, exclusive of the anal forceps ; 

 but, in the female it will be perceived, that although, with 

 great care, the nine segments be discoverable, two of the ter- 

 minal ones have assumed a rudimental appearance. The ab- 

 domen of some beetles exhibits a curious character in this 

 respect. Thus in Carahus, if the under surface of the abdo- 

 men only be examined, it would appear that there are but five 

 abdominal segments ; but if the back of this part be viewed, 

 nine joints will be discovered : another peculiarity exists in 

 the stinging Hymenoptera, in which the males have seven and 

 the females only six abdominal segments. The union of the 

 abdomen A^dth the thorax is effected in two different modes 

 in the different groups. Thus, in all insects which have the 

 wings defended by mng-covers, hemelytra, or tegmina (beetles, 

 bugs, tree-hoppers, &c.), as well as in many insects with en- 

 tirely membranous wings, the base of the abdomen is as large 

 as the extremity of the metathorax, and is united to it by 

 membrane throughout its entire breadth or circumference, 

 in which case the abdomen is said to be sessile. In the hy- 

 menopterous order, the saw-flies and Siricidce are distin- 

 guished by this character from the other tribes. In the 

 other mode, the abdomen is connected with the thorax only 

 by a slender portion of its base, and this is the case with 

 those insects to which I have alluded in the account of the 

 curious apparatus for elevating the abdomen, in describing 

 the metathorax. Insects thus distinguished are divisible 

 into two sections ; first, those in which the union is effected 

 by a very short piece, and the abdomen is as broad as the 

 posterior part of the thorax, so that, as in the hairy-bodied 



