INSECTS OF NEW-YORK. 



CHAPTER I. 



GENERAL CONSIDERATIONS. 



The common idea of an insect is, probably, sufficiently exact for all practical purposes ; 

 yet it seems proper that the scientific idea should be expressed : indeed it is always im- 

 portant to define clearly the limits of all departments of Natural History, by stating in 

 determinate language the boundaries which confine them. Insects, then, are animals whose 

 bodies are covered with a coriaceous integument ; and they are divided into three distinct 

 segments or sections, the head, thorax, and abdomen. The head is provided with two an- 

 tennae ; the thorax, with six articulated legs ; and the abdomen with many rings, and 

 contains the digestive organs : the sexes are distinct. They have a respiratory, circulatory 

 and nervous apparatus : the first permeates the whole body ; the second consists mainly 

 of a long vessel extending through the body, and is called a dorsal vessel, from the 

 position it occupies ; the third is a symmetrical arrangement of nervous threads in two 

 lines, placed upon the abdominal face, and connected by knots or ganglia at every ring of 

 the body. The breathing is performed through small openings along the sides of the ab- 

 domen, at every ring : the air admitted permeates the whole system, and acts upon the 

 fluids as in all animals. The most interesting peculiarities, however, consist in the changes 

 which the insect undergoes during its stages of growth, which, although the developments 

 are not more remarkable than in other departments of the animal kingdom, yet differ from 

 the higher in being stationary for certain periods, during which it performs the functions 

 of a perfect animal, except indeed that which belongs to the exercise of the sexual or- 

 gans. These changes are called metamorphoses, and consist of three stages, the worm or 

 larva, the pupa, and the perfect insect. 



[ Agricultural Report — Vol. v.] 1 



