ANNULOSA: INSECTA. 



209 



maxillae, tlie hinder pair of which are coalescent, and form the 

 " labium." Three, or perhaps, in some cases, more, somites 

 unite and become specially modified to form the thorax, to 

 which the three pairs of locomotive limbs, characteristic of 

 perfect Insects, are attached. Two additional pairs of loco- 

 motive organs, the wings, are developed, in most insects, 

 from the tergal walls of the second and third thoracic somites. 

 No locomotive limbs are ever developed from the abdomen of 



Fig. 61. Diagram of Insect, a. Head, carrying the eyes and antennae; 6. 

 Prothorax, carrying the first pair of legs ; c. Mesothorax, carrying the 

 second pair of legs and first pair of wings ; d. Metathorax, with the third 

 pair of legs and the second pair of wings ; e. Abdomen, without limbs, but 

 having terminal appendages subservient to reproduction. 



the adult insect, but the ventral portions of the abdominal 

 somites, from the eighth backwards, are often metamorphosed 

 into apparatuses ancillary to the generative function.' 

 (Huxley.) 



The integument of the Insecta, in the mature condition, is 

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

 forms a resisting exoskeleton, to which the muscles are at- 

 tached. 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 



VOL. i. p 



