222 INSECTS. 



spines, and calculated for digging in the earth ( pedes fossorii.) 

 These feet also in some are not subservient to motion, as in many 

 Papilionides, and they differ in others according to the sexes. 



The abdomen, forming the third and last part of the body, 

 includes the viscera and sexual organs. It is composed of from 

 six to nine segments, each divided into two semicircles or plates 

 united laterally, the under portion being termed the belly. 

 The parts of generation are situate at the posterior extremity ; 

 and hooks or forceps of different forms accompany these parts 

 in the male. The oviduct of many females is prolonged be- 

 yond the termination of the abdomen, sometimes in the form of 

 an articulated tube ; sometimes as an ovipositor or auger (tere- 

 bra,) composed of plates or filaments often dentated at the end. 

 This oviduct terminates in a sting (aculeus) in the females and 

 neuters of many Hymenoptera. 



The exterior envelope of insects, which is more or less solid, 

 serves the double purpose of outward protection and internal 

 support. Less complicated than the skin of the higher classes, 

 it seems to consist of but two layers, the epidermis or outer skin, 

 and the mucous tissue. Detached from the mucous tissue, the 

 epidermis of insects is almost pellucid or semitransparent and 

 colourless. From its manner of growth and the great propor- 

 tion of gelatine in its composition, the substance of the outer 

 envelope is of a horny consistence, more flexible than the co- 

 verings of the Crustacea, where the phosphate of lime predomi- 

 nates over the animal matter. The body of a caterpillar de- 

 prived of the epidermis presents the same colours as before ; and 

 it is conceived that the growth of the epidermis, being stopped 

 by the layers which grow successively below, destroy the func- 

 tions of the envelope, and occasion the change of covering ob- 

 served to take place in the animals at this stage. The appen- 

 dages of the skin consist of spines, hairs, and scales, the first 

 two being merely prolongations of the epidermis. 



The solid soft parts are in insects of two kinds. The first, 

 termed muscles, are formed of soft fibres, disposed in bundles, 

 capable of producing motion by their contraction in the parts 

 to which they are affixed. These muscles are always attached 

 to the harder parts by a tendon of a horny consistence. The 

 other soft parts, formed also of muscular fibre, constitute the 

 interior organs, which, with the fluids, perform the necessary 



