58 DR. HARRIS’S REPORT. April, 
Habits of some of the Insects injuriousto 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; with no vertebre nor internal 
bony skeleton ; without organs of circulation ; respiring by lateral 
pores or spiracles and trachee ; undergoing a metamorphosis of three 
stages before arriving at the perfect state ; and in that state having 
six legs only, a distinct head, immovable compound eyes, a pair of 
antenne, 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 
