ORDERS OF INSECTS, 165 
CHAPTER XVIII. 
ORDERS OF INSECTS. 
THE known number of insects is so enormous, their forms are 
so various, and their habits and instincts are not only so re- 
markable, but have been so fully described, that it were hope- 
less to attempt here to do more than give the briefest possible 
outline of the leading characters which distinguish the different 
orders. The student desirous of further information on this head 
must have recourse to treatises specially devoted to entomology. 
SECTION I. AMETABOLIC INSECTS.—Young not passing 
through a metamorphosis, and differing from the adult im size 
only. Perfect insect (imago) destitute of wings; eyes simple, 
sometimes wanting. 
ORDER I. ANOPLURA.—The insects comprised in this order 
are parasitic upon man and other animals, and they are com- 
monly known as Lice. They are all very minute in size, desti- 
tute of wings in the adult state, having a mouth formed for 
suction, and having either two simple eyes or none, 
ORDER II. MALLOPHAGA, —These are known as “ Bird-lice,” 
and are all minute parasites on different birds. ‘They are dis- 
tinguished from the true lice by not living upon the juices of 
their hgst, but upon the more delicate and tender appendages of 
the skin. The mouth is, consequently, not suctorial, but fitted 
for biting. 
ORDER III. THYSANURA.—The most familiar members of this 
order are the “ Spring-tails” (Podure@), which are commonly 
found under stones or in cellars and suchlike situations. They 
are distinguished by having the extremity of the abdomen fur- 
