THE INSECTA. 57 



Of these five certainly, and six probably, constitute the head, 

 which possesses a pair of antennae, a pair of mandibles, and two 

 pairs of maxillae; the hinder pair of which arc coalescent, and 

 form the organ called 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 locomotive 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 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 (Figs. 28 and 29). 



* The female Stylops is stated to possess no thoracic limbs. 



