INSECTS. 71 



of leaping insects ; 3, of the thin, long tibia, united with^the thigh 

 by a hinge-joint ; and, 4, the foot == tarsus, which is rarely eight- 

 jointed, usually composed of five joints, with the joints dilated, 

 beset with balls, brushes, or warts on the lower surface, and 

 with the last joint furnished with two, or rarely with one, 

 curved, sharp, horny claw, which is very seldom deficient. The 

 legs are adapted for digging, leaping, swimming, seizing prey, 

 walking, or running. 



3. The abdomen exhibits a still more distinct annulation than 

 the head and chest. The rings consist of an upper and lower 

 arch, which are united at the sides and above and below, and 

 between the scaly layers of the segments, by elastic skin. The 

 normal number of abdominal segments appears to be nine ; but 

 this is often unrecognisable by the sliding of the last segments 

 into each other. They have no legs, but in some the immove- 

 able bristles serve as leaping organs. 



The skin is of various degrees of hardness, consists of chitine, 

 which is so difficult to destroy chemically, and often perfectly 

 homogeneous and structureless, but frequently deposited in strata, 

 furnished with bristles, hairs, &c., attached more or less firmly 

 on the outside, and internally with processes for the attachment of 

 the muscles. 



The muscles are transversely striated, like the voluntary muscles 

 of the higher animals, but in the duration and efficacy of their 

 action accomplish much more than could be expected from their 

 mass. 



The nervous system consists of a series of ganglia, which is 

 united by two longitudinal filaments, and always lies upon the 

 lower integument. In the head there is a brain with the antennal 

 and optic nerves, which gives off two filaments downwards to form 

 an oesophageal ring; from this pass off longitudinal filaments, 

 which are sometimes separated, sometimes more coalescent, in 

 accordance with the structure of the segments themselves. Besides 

 the ventral cord there is a separate intestinal nervous system (two 

 nerves forming a pair and a median one) for the oesophagus and 

 stomach. 



The sense of touch is abundantly provided for by the antenna, 

 the palpi, the apex of the proboscis, the female ovipositors, and 

 the tarsi. The organ of taste is unknown, as are also the organs 

 of hearing, with the exception of the ears of the Orthoptera. 



The alimentary canal is always intestiniform, of very various 



