STRUCTURE OF INSECTS. 



63 



merits are closely united, but the natural distinction between 

 them is marked by a transverse line. 



169. The third principal division is the abdomen. Fig. 

 53. This in the instance before 



us, is composed of six complete, 

 and three imperfect segments, but 

 these segments vary in number in 

 different insects, from three or four, 

 to twelve or more. These segments 

 all have a ligamentous connexion 

 with each other, allowing free mo* 

 tion in all directions. 



170. The limbs of insects are 



named from their supposed analogy to corresponding parts 

 in the higher order of animals. Thus the haunch, h, cor- 

 responds to the hip-bone of quadrupeds ; the trochanter, t, 

 to the head of the thigh-bone ; the femur,/, to the thigh- 

 bone itself ; the tibia, s, to the bones of the leg ; and the 

 tarsus, r, to those of the foot. 



171. It is perhaps unnecessary, in a work like the pres- 

 ent, to give a detailed account of the peculiar mechanism, 

 motions, and uses of each of these parts. The limbs of in- 

 sects down to the feet, may be considered as acting in a 

 manner analogous to our own. The feet have peculiarities 

 to which there is no analogy in other animals, and which, 

 therefore, must receive further notice. 



172. The legs of most insects diverge, so as to reach 

 considerably beyond their bodies on each side, thus giving 

 them a firmer support, by throwing the centre of gravity 

 far within the base. When the legs are very long, the 

 insect, therefore, appears rather suspended, than supported 

 by them, contrary to what obtains in quadrupeds and man, 

 where the feet are immediately below the points where the 

 legs are connected with the body. 



173. In insects, the last joint of the tarsus is generally 

 terminated by a claw, sometimes single, and sometimes 

 double, and by which the foot is fastened in walking to 

 any surface which is in the least degree rough, or unequal. 

 By these hooks, insects also suspend themselves on perpen- 

 dicular surfaces, or with their backs downward, this being 



By what means do insects walk on rough surfaces * 



