168 INVERTEBRATE ANIMALS. 



CHAPTEE XVII. 



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 remarkable, 

 but have been so fully described, that it were hopeless to attempt 

 here to do more than give the briefest possible outline of the lead- 

 ing 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 pasmig through a 

 Ttietamorphosis, and differing from the adult in size only. Perfect 

 insect or imago destitute of wings; eyes simple, sometimes wanting. 

 Owing to the fact that the adult ametabolic insects have no wings, 

 they are often grouped together as a common assemblage, under the 

 name of Aptera. 



Order I. Anoplura. 



The insects comprised in this order are parasitic upon man and 

 other animals, and they are commonly knowTi as Lice (Pediridits, 

 fig. 11.3, A). They are all very minute in size, destitute of wings 

 in the adult state, having a mouth formed for suction, and having 

 either tWo simple eyes or none. 



Order II. Mallofhaga. 



These are known as " Bird-lice," and are all minute parasites on 

 different birds or quadrupeds (fig. 113, B). They are distinguished 

 from the triie Lice by not living upon the juices of their host, but 

 upon the more delicate and tender appendages of the skin. The 

 mouth is, consequently, not suctorial, but fitted for biting. 



