158 



INVERTEBRATE ANIMALS. 



SECTION III. HOLOMETABOLA. Metamorphosis complete ; 

 the larva, pupa, and imago, differing greatly from one an- 

 other in external appearance. The larva worm-like, and the 

 pupa quiescent. 



ORDER VII. APHANTPTERA (Gr. aphanos, inconspicuous ; 

 pteron, wing). In this order are only the Fleas (Pulicidce), in 

 which the mouth is suctorial, the metamorphosis is complete, 

 and the wings are rudimentary, being represented by four 

 minute scales placed on the last two segments of the thorax. 

 The larva of the common flea is a footless grub, which in 

 about twelve days spins a cocoon for itself, and becomes a 

 quiescent pupa, from which the imago emerges in about a 

 fortnight more. 



ORDER VIII. DIPTERA (Gr. dis, twice ; pteron, wing). 

 The insects of this order, as implied by its name, have only a 

 single pair of wings namely, the anterior pair. The poste- 

 rior wings are rudimentary, and are represented by two 



FIG. 70. Diptera. Crane-fly (Tipula oleracea). 



clubbed filaments called " balancers " or " poisers " (Fig. 70). 

 The mouth in the Diptera is suctorial. 



