DIVISION II. APTEROUS INSECTS. 



734. BESIDES the foregoing Orders, we must include three 

 others in the Class of Insects, on account of their correspondence 

 with it in general structure ; although they present only one, or 

 even neither, of the two characters which have been stated to be 

 its peculiar distinctions, namely, the presence of wings in the 

 perfect state, and the metamorphosis. 



ORDER IX. APHANIPTERA. 



735. OF the three Apterous orders, this one undoubtedly 

 approaches nearest to the true Insects ; for we find in it a 

 metamorphosis, and even rudiments of wings ; whilst the struc- 

 ture of the mouth most nearly approaches that of the Diptera. 

 The Fleas and their allies, 

 which constitute this order, 

 resemble the Diptera also in 

 their suctorial habits ; and 

 feed exclusively upon animal 

 juices. Their larvae come 

 forth from the egg in the state 

 of minute worms, possessing 

 considerable activity, and FlG . 431 . _ THE FLBA . (Pulex irritan ^ 

 feeding upon animal matter, 



in the midst of which the eggs were deposited by the parent. 

 They afterwards enclose themselves in a small cocoon of silk, 

 which is often covered with dust ; and in this they undergo their 

 change into the Pupa state. In the Imago, the rudiments of 

 wings are visible, in the form of little scales, attached to the 

 second and third segments of the body ; there is, however, no 

 proper distinction of thorax and abdomen. The Common Flea 



