PHYLUM ARTHROPOD A 



639 



mandibles and maxilla?. In the Diptera (Fig. 517) the mandibles 

 (md.), usually not developed in the males, are biting or piercing 

 organs, while the basal parts of the labium form a proboscis (mir^) 

 enclosing a spine or seta (Ap.)— which is a process from the hypo- 

 pharynx, a chitinous process on the floor of the mouth — and 

 sometimes stylet-like maxillae {mo^.). In the Lepidoptera (Fig. 

 518) the mandibles are aborted in the adult, and the maxillaj are 

 developed into elongated half-tubes, which when applied together 

 form a complete tube (.sr.) capable of being coiled up in a spiral 

 manner under the head, 

 the extremity provided 

 with hooks or spines for 

 rupturing the nectaries of 

 flowers. 



Appendages of the 

 thorax — Each of the seg- 

 ments of the thorax bears 

 a pair of five-jointed legs ; 

 the terminal section or 

 tarsus being made up of a 

 number of short segments 

 and ending in a pair of 

 claws, often Avith an ad- 

 hesive pad or sucking disc 

 between them. In accord- 

 ance with variations in 

 the uses to which they are 

 put, considerable differ- 

 ences are observable in the 

 form of the legs in different 

 groups of Insects. In most 

 they are adapted for walk- 

 ing, and are long and 

 slender; in some they 

 are expanded to enable 

 them to act as swimming 

 paddles ; in some the first 

 pair are prehensile, and develop a sub-chelate extremity ; in 

 others, again, the legs, or the first pair of them, are stout and 

 adapted for burrowing. In addition to the legs the meso- and 

 meta-thorax may each bear a pair of wings. The wings are thin 

 transparent expansions of the integument of the body, supported 

 by a system of branching ribs or nervures consisting of chitinous 

 material with branches of the trachese, nerves, and tubular diver- 

 ticula of the body-cavity. In most Lepidoptera the wings are 

 opaque, owing to their being covered with numerous overlapping 

 microscopic scales, to which the various colours of the wing are 



Pig. 518.— Mouth parts of the Iiepidoptera. B, the 

 second maxillEB. Lettering as in preceding figures ; 

 ■j>L labial palp ; jmi. palp of the anterior maxillie ; 

 sj'. sucliing tube. (From Lang.) 



