TYPE TEACHEATA. 509 



somewhat complicated system of chambers, galleries, and 

 storehouses. 



To this group belong also the Psocidce and the Mallophaga. 

 The former are small forms found upon the leaves of various 

 trees and occasionally in houses. They do not show poly- 

 morphism and are usually provided with wings, though the 

 genus Atropos, not uncommon in books which have remained 

 long undisturbed, lacks them. The Mallophaga are all 

 destitute of wings and are parasitic, living upon the bodies of 

 birds (Liotlieum], whence they are usually termed the Bird-lice. 

 They feed upon the feathers and are comparatively active in 

 their movements. A few forms occur on mammals, e.g. 

 Trichodectes on the dog. 



The larvae of all these forms resemble the adults except in 

 size and in the absence of wings, and the metamorphosis is 

 gradual. Since the Mallophaga are destitute of wings in the 

 adult condition they may properly be said to be secondarily 

 ametabolic. 



7. Order Thysanoptera. 



The Thysanoptera are small Insects which live upon the 

 leaves of various plants, which they pierce for the purpose of 

 obtaining nutrition, and sometimes are very injurious to 

 wheat, clover, and other cultivated plants. The wings are 

 narrow, but imperfectly veined, and with the edges fringed 

 with numerous slender hairs ; they are, however, occasionally 

 wanting. The antennae are short and filiform and the mouth- 

 parts intermediate between the biting and the sucking type. 

 The mandibles are reduced to styletlike piercing-organs and 

 are enclosed within a tubular proboscis formed by the fusion 

 of the labrum with the maxillae and labium, both of these last 

 appendages retaining their palps and showing usually their 

 typical parts. The legs are adapted for rapid locomotion and 

 are peculiar in that the terminal joint of the tarsus, instead of 

 bearing ungues, is provided with a protrusible sac which 

 serves for adhesion ; on account of this peculiarity the order 

 is sometimes known as the Physapoda. 



The larvae except for the absence of wings are closely 



