ANNULOSA: INSECTA. 



249 



more or less hardened ,by the deposition of chitine, and usually 

 forms a resisting exoskeleton, to which the muscles are attached. 

 The segments of the head are amalgamated into a single piece, 

 ■which, bears a pair of jointed feelers or antennae, a pair of eyes, 

 usually compound, and the appendages of the mouth. The 

 segments of the thorax are also amalgamated into a single 

 piece ; but this, nevertheless, admits of separation into its con- 

 stituent three somites (fig. 83). These are termed respect- 

 ively, from before backwards, the "prothorax," "mesothorax," 

 and " metathorax," and each bears a pair of jointed legs. In 

 the great majority of Insects, the dorsal arches of the mesotho- 

 rax and metathorax give 



origin each to a pair of 

 wings. 



Each leg consists of from 

 six to nine joints. The 

 first of these, which is at- 

 tached to the sternal sur- 

 face of the thorax, is called 

 the "coxa," and is suc- 

 ceeded by a short joint 

 termed the "trochanter." 

 The trochanter is followed 

 by a joipt, often of large 

 size, called the "femur," 

 and this has articulated 

 to it the " tarsus," which 

 may be composed of from 

 two to five joints. 



The wings of Insects 

 are membranous "flatten- 

 ed vesicles, sustained by 

 slender but firm hollow 

 tubes, called ' nervures,' 

 along which branches of 

 the tracheae and channels 

 of the circulation are con- 

 tinued." — (Owen.) Ac- 

 cording to Newport, the 



Fig. 83. — Di^gl^am of Insect, a Head, carrj'ing 

 the eyes and antennae; ^Prothorax, carrying 

 the first pair of legs; r Mesothorax^ carrj'ing 

 the second pair of legs and first pair of wings ; a 

 Metathorax, with the third pair of legs and the 

 second ^air of wings ; e Abdomen, without limbs, 

 but haym^ terminal appendages subservient to 

 reproduction. 



wings of Insects are "expanded portions of the common in- 

 tegument of the sides of the meso- and meta-thorax, occasioned 

 by the erjajcgement and extension of numerous tracheae and 

 the accompanying passages for the circulatory fluids, and their 

 motions are intimately connected with the function of respira- 

 tion," In the Coleoptera (Beetles) the anterior pair of wings 



