INSECTS. — GENERAL CHARACTERISTICS. 3 



interested in ngricnltnral pursuits. For tlieir use, chiefly, 

 this account of tlie principal insects that are injurious to 

 vegetation in Xew Enghmd, lias been prepared. It has 

 been thought best to prefix thereto some remarks on the 

 structure and classification of insects, to serve as an intro- 

 duction to the succeeding chapters, and, in some measure, 

 to su[)})ly the Avant of a more general and complete work 

 on this branch of natural history. 



The wortl Insect, which, in the Latin language, from 

 whence it was derived, means cut into or notched, was 

 designed to express one of the chief characters of this 

 group of animals, whose body is marked by several cross- 

 lines or incisions. The parts between these cross-lines are 

 called segments, or rings, and consist of a number of jointed 

 pieces, more or less movable on each other. 



Insects have a very small brain, and, instead of a spinal 

 marrow, a kind of knotted cord, extending from the brain to 

 the hinder extremity ; and numerous small whitish threads, 

 which are the nerves, spread from the brain and knots, in 

 various directions. Two long air-pipes, within their bodies, 

 together with an immense number of smaller pipes, su})plv 

 the want of lungs, and carry the air to every part. Insects 

 do not breathe through their mouths, but through little 

 holes, called spiracles, generally nine in number, along each 

 side of the bodv. Some, however, have the breathing-holes 

 placed in the hinder extremity, and a few young water- 

 insects breathe by means of gills. The heart is a long tube, 

 lying under the skin of the back, having little holes on each 

 side for the admissi(^n of the juices of the body, which are 

 prevented ft-om escaping again by valves or clappers, formed 

 to close the holes within. Moreover, this tubuhu- heart is 

 divided into several chambers, by transverse partitions, in 

 each of which there is a hole shut by a valve, which allows 

 the blood to flow only from the hinder to the fore part of the 

 heart, and prevents it ft'om passing in the contrary direction. 

 The blood, which is a colorless or yellow fluid, does not cir- 



