INSECT. 



868 



form in the individuals of different sexes of the same 

 species. They are often formed for seizing the prey 

 of the insect, and are then called raptorial (pedes 

 raptorii}, the thigh being thickened and spined, and 

 the tibia closing upon it. The hind legs are also often 

 peculiarly organised, as in the bees, where they are 

 pollinigerous (pedes polliniferi), or in the grasshop- 

 pers, &c., where the femora are greatly thickened, 

 and used in leaping (pedes saltatorn, fig. 137)*. In 

 some other insects they are terminated by abroad, Bat- 

 tened, and strong ciliated tarsus, admirably formed 

 for swimming, as in the water-beetles (pedes natatorii, 

 fig. 188). The tibia in the anterior legs are often 

 dilated and notched on the outer edge, as in the mole- 

 cricket. These legs thus become proper for burrow- 

 ing (/ rii. See our article ENTOMOLOGY for 

 figures of these variations of legs). In some lepido- 

 pterous insects, especially amongst the butterflies be- 

 longing to the family Nymphalida:, the fore-legs are 

 very short and rudimental, the tarsi being almost 

 obliterated, and quite unfitted for walking. In some 

 insects the various parts of the leg fold upon each 

 other when unemployed, and are there received into 

 certain channels prepared for their reception on the 

 under side of the thorax. This is the case with the 

 pill-beetles (Byrrhid&\ mimic-beetles (Histeridce), &c. 

 As regards the relative proportions of the legs of 

 insects, the general rule is, that the anterior are the 

 shortest, and the posterior the longest ; and as re- 

 gards their length, the shorter and more robust the 

 body, the shorter are the legs, and vice versa. In 

 running insects, also, the legs are longer than in those 

 which crawl. Generally, the legs do not much ex- 

 ceed the body in length, but occasionally they are 

 much longer. As regards their direction, the ante- 

 rior legs are generally directed forwards, and the four 

 posterior backwards. It would occupy far too much 

 space were we to enter into a detailed notice of all 

 the variations in form which occur in the legs of 

 insects. 



C The abdomen, or tfie seat of the organs of genera- 

 tion. We have now arrived at the third and last 

 principal division of the body which encloses the 

 greater portion of the intestines, the organs of gene- 

 ration, and their appendages. Unlike the preceding 

 part of the body, the abdomen, from being destitute 

 of locomotive organs, necessarily exhibits a much 

 less complicated organisation in the various segments 

 of which it is composed than those of the thorax, and 

 typically consits of nine segments, exclusive of 

 the anal apparatus, each being composed of two arcs, 

 or half segments, one upper and the other under. 

 These rings are attached together by membrane, and 

 either meet at the edges, or slide into each other like 

 the tubes of a telescope. The dorsal one is termed the 

 back (dorsnm), and the ventral one the belly {venter). 

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

 segments exist which are not found in the imago ; and 

 the examination of the abdomen in various insects 

 clearly proves that these last segments are abdominal 

 ones. Thus, if a male ear-wig 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 

 terminal ones have assumed a rudimental appearance. 



* We must refer to the article CfiRCOPtofl?, where we have 

 entered into various details relative to this subject. 



The abdomen of some beetles exhibits a curious cha- 

 racter in this respect. Thus, in Carabus, if the under 

 surface of the abdomen be only 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 ffymcnoptera, in which the males have seven, 

 and the females only six abdominal segments. The 

 union of the abdomen with the thorax is effected in 

 two different modes in different groups. Thus, in all 

 insects which have the wings defended by wing- 

 covers hcmelytra, octeginina, (beetles, bugs, tree-hop- 

 pers, &c.), as well as in many insects with entirely 

 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 hymenopterous order, 

 the saw-flies and Siricidee are distinguished 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 we have alluded in our account 

 of the curious apparatus for elevating the abdomen, 

 in our account of the metathorax. Insects thus dis- 

 tinguished 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 bees, it 

 appears to be affixed by its entire breadth ; and, 

 second, those in which the connecting piece is elon- 

 gated into a peduncle, and the base of the abdomen 

 itself narrow. This is the case with many exotic 

 wasps, sand wasps (AmmopMla], &c. In the latter 

 division the abdomen is said to be pedunculated or 

 petiolated. The peduncle itself is liable to great 

 variation. Thus, in some ants, it consists of two 

 knots (petilus binodosus) ; in others only of one. 

 Sometimes it is disproportionately long ; at other 

 times it is saucer-shaped, bell-shaped, &c. Of the 

 shape of the entire abdomen little in general can be 

 said. It is, however, more generally triangular, 

 ovate, or quadrate, with the posterior angles rounded 

 off ; generally, too, the upper surface is more or less 

 depressed ; sometimes it is very short, at others dis- 

 proportionately long ; sometimes wider than the 

 thorax, but more commonly narrowed. The extre- 

 mity of the abdomen is generally pierced by the anal 

 aperture. The terminal segment is very variable in 

 its form, being formed with reference to the coupling 

 of the insects, or to facilitate the disposition of the 

 eggs in appropriate situations. Sometimes, also, it is 

 organised in a manner to become an instrument of 

 defence or offence. The various organs to be noticed 

 below form part of this segment. It still remains for 

 us to notice the motions of this part of the body. 

 Unlike the thoracic segments, which, from bearing 

 the organs of locomotion, are necessarily required to 

 be as firm as possible, and are not, consequently, 

 capable of much distinct motion, the abdominal seg- 

 ments being destitute of such organs, and having im- 

 portant functions to perform, are, on the contrary, 

 gifted with a considerable but variable degree of mo- 

 tion. Thus, in those species which have the extre- 

 mity of this part of the body furnished with offensive 

 or defensive instruments, it is capable of very consi- 

 derable movements in every direction. This is the 

 more noticeable in insects which have a very much 

 elongated abdomen ; as. for instance, the ear-wig, 



