25o INSECTS. PHYLUM ARTHROPODA 



midges (Chironomids), and daddy-long-legs or crane flies 

 (Tipulidje), the larvae of which are leather- jackets. 



The above five orders of the Endopterygota are sometimes 

 regarded as being much more closely related to each other than 

 are the remaining three ; they may have been derived from a 

 common ancestor which was not unUke a member of the 



Mecoptera. 



Order 22. Aphaniptera. The fleas, such as Pulex irritans, the 

 human flea (Fig. 192), are ectoparasites of mammals and have 

 piercing and sucking mouth-parts. There are no wings, and the 

 body is strongly laterally compressed. The adults, which alone 

 suck blood, can live for a short time away from their host, and 



c 



B. 



A. 



Fig. 192. — ^The Common Flea {Pulex irritans) x c. 12. 

 A, Larva ; B, pupa ; C, adult. 



leave him to lay their eggs. The larvse have biting mouth-parts, 

 and feed on organic matter in dust. Pulex irritans pupates in a 

 cocoon after a larval life of about twelve days. The rat flea, 

 Xenopsylla cheopis, which occasionally sucks the blood of man, 

 carries the germ which causes bubonic plague. 



Order 23. Coleoptera. The beetles (Fig. 193) are a very large 

 order of insects of a characteristic form, easily recognised by the 

 straight longitudinal line made by the meeting of the wing cases. 

 The mouth-parts are biting, and the fore wings are modified 

 as hard elytra. The larvse are of various types, and hypermeta- 

 morphosis sometimes occurs. 



Order 24. Strepsiptera. These insects are small, with degenerate 

 biting mouth-parts, and are perhaps derived from the beetles. 

 The larvse and usually the adult females are endoparasites of 

 other insects, and the males have the fore wings reduced to knobs. 



Order 25. Hymenoptera. This is an important order, including 

 ants, sawflies, wasps, and bees. The mouth-parts are primarily 



