58 DR. HARRIS'S REPORT. April, 



Habits of some of the Insects injurious to Vegetation in Massachusetts. 



Insects are divided by popular writers into those which are injuri- 

 ous, and those which are beneficial to mankind. The former are 

 appropriated to man and animals, or derive their sustenance from 

 vegetables ; the latter are destined to balance the account by keeping 

 in check the noxious insects, or by contributing directly to man's 

 convenience. 



The science of Entomology is of great importance in enabling us 

 to detect our enemies, and discriminate our friends of the insect race. 



In this portion of the Report, it is proposed to give an account of 

 a few insects injurious to vegetation in this vicinity. It will be proper, 

 however, first to explain some of the terms that must necessarily be 

 used. 



Insect^ in Latin insectum, is an abbreviation of intersectum ; the 

 body of insects being intersected or divided into segments. An 

 insect is an animal with a double, knotted, medullary chord ; a body 

 divided transversely into segments ; vviih no vertebras nor internal 

 bony skeleton ; without organs of circulation ; respiring by lateral 

 pores or spiracles and trachefe ; imdergoing a metamorphosis of three 

 stages before arriving at the perfect state ; and in that state having 

 six legs only, a distinct head, immovable conripound eyes, a pair of 

 antennas, and (with few exceptions) furnished with organs of flight. 

 You probably know, that in man and quadrupeds the nervous system 

 consists of a brain, spinal marrow, and the nerves which branch from 

 them. In insects the brain is minute, but, to compensate for this, 

 there issues from it a double medullary cord, dilating at intervals 

 (usually corresponding with the segments) into knots or ganglions 

 which give origin to the nerves. 



In man and quadrupeds the spinal marrow is enclosed in a bony 

 case, composed of several joints, which, united, form the back-bone 

 or spine, and the whole body is built upon an osseous frame or skel- 

 eton. Insects have no bones, their external skin being sufficiently 

 hard to give firmness and support to their bodies. 



Insects have not an uninterrupted circulation of blood from a heart 

 through arteries and veins. A longitudinal vessel, situated under the 



