INSECTS. — GENERAL CHARACTERISTICS. 
3 
interested in agricultural pursuits. For their use, chiefly, 
this account of the principal insects that are injurious to 
vegetation in New England, has 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 supply the want of a more general and complete work 
on this branch of natural history. 
The word 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, supply 
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 body. 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 admission of the juices of the body, which are 
prevented from escaping again by valves or clappers, formed 
to close the holes within. Moreover, this tubular 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 from passing in the contrary direction. 
The blood, which is a colorless or yellow fluid, does not fir- 
