'264 MANUAL OF ZOOLOGY. 



which is the special object and care of the remainder. No 

 higher development could well be imagined amongst creatures 

 devoid of the higher psychical endowments ; and it is worthy 

 of note that at least three distinct and independent families of 

 Insects have attained to this stage — namely, the Termites, the 

 Bees, and the true Ants. 



Sub-class III. Holcmetabola.- — Metamorphosis complete; 

 the larva,pupa^ and imago differing greatly from one another in ex- 

 ternal appearance. The larva vermiform, and the pupa quiescent. 



Order VII. Aphaniptera. — Wings rudimentary, in the 

 form of plates, situated on the meso-thorax and meta-thorax. 

 Mouth suctorial. Metamorphosis complete. 



This order comprises the Fleas (Pulicidce), most of which 

 are parasitic upon different animals. The larva of the common 

 Flea is an apodal 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. Besides the 

 common Flea {Pulex, irritans), another well-known and con- 

 siderably more troublesome member of this order is the Chigoe 

 {Pulex penetrans) of the West Indies and South America. 



Order VIII. Diptera. — The anterior pair of wings alone 

 developed ; the posterior pair of wings rudimentary, re- 

 presented by a pair of clubbed filaments, called "hal- 

 teres," or "balancers'' (fig. 92). In a few the wings are 

 altogether wanting. Mouth suctorial. The metamorphosis 

 is complete, the larvas being generally destitute of feet ; but 

 in some cases (e.g., the gnats) the pupae are aquatic and are 

 actively locomotive. In most cases, however, the pupae are 

 quiescent. 



The proboscis in the Diptera consists of a tubular labium, 

 enclosing the other parts of the mouth, and is placed on the 

 under surface of the head. Ocelli are present in addition to 

 the compound eyes. The wings are generally horizontal and 

 transparent, the nervures not very numerous, and for the most 

 part longitudinally disposed. The antenns are generally 

 small and three-jointed, sometimes many-jointed (Tipulidce), 

 or feathery ( Culiddce). The larva is soft and fleshy, with a 

 soft indistinct head, usually apodal, never with thoracic legs, 

 and rarely with pro-legs. The larval skin mostly forms a 

 hardened case for the pupa, but the larvae sometimes cast 

 their skin when becoming pupas, or even spin cocoons. In 

 some the eggs are hatched within the body of the mother, so 

 that the insect appears first in the larval state ; and in Pupipara 

 not only is this the case, but the larvae continue to reside with-' 

 in the mother until they become pupae. 



