CHAPTER XXXVI. 



INSECT A. 



THE forms of life already studied have been for the most part 

 water animals of such low organism and retiring habits that 

 they have never forced themselves upon the notice of mankind. 



But insects are air-breathing animals abounding everywhere, 

 in the air and soil, in our homes and workshops; they are para- 

 sites inside the human body, and often find an abiding place on 

 the outside; they bite and sting and irritate and annoy by night 

 and by day, and so persistent and aggressive are they in their 

 work that only occasionally can humanity turn aside from the 

 irrepressible conflict to notice that insects are intelligent, that 

 some are exceedingly beautiful, that some are useful, and that 

 insects as a class fill an important niche in the scheme of nature. 



Insects are very numerous, outnumbering by far all other 

 forms of animal life; and while they differ widely in size, form 

 and mode of life, they are usually easily distinguished from 

 other kinds of life. Among the insecta there is a well-marked 

 division of the body into head, thorax and abdomen. 



The head appears to be composed of but one mass, but many 

 think it really a consolidation of four segments. The appen- 

 dages of the head are the eyes, the antennae and the mouth 

 parts. The simple eye or ocellus consists of a convex cornea 

 resting on a crystalline lens, which in turn rests on a vitreous 

 humor, forming quite a complete eye; the compound eye is but 

 a collection of these simple eyes. Some think the ocelli are used 

 in the perception of nearer objects. The antennae are tubular 

 bodies well supplied with nerves, seeming to be organs of touch, 

 often appearing to be organs of hearing and smell. They differ 

 widely in form and size. 



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