cs 
INTRODUCTION TO 
which it is derived, is exactly synonymous with the 
Greek one tvrofia 3 from which we obtain the princi- 
pal component part of the term Entomology .* 
Both words therefore are sufficiently descriptive 
of the whole articulated races, and, in fact, when 
originally applied, were designed to embrace them 
all. In the more limited and precise sense in which 
it is now used, the word insect is applied to such 
animals only as present the following characters : — 
no internal skeleton ; a nervous system composed of 
ganglions ; an imperfect circulating system ; respi- 
ration by means of tracheae communicating with the 
air by stigmata ; oviparous, the sexes distinct ; body 
covered by a coriaceous or membranous integument, 
and divided into three distinct sections, viz. the head, 
provided with two an ten use ; the thorax, with six 
articulated legs ; and the abdomen, usually having 
the sexual organs at the extremity ; and, finally, not 
presenting these parts in full developement till after 
having passed through (with very few exceptions,) 
several successive changes called metamorphoses . t 
These negative and positive characters, derived 
both from external and internal parts, will be found 
distinctive, and completely exclusive of all the other 
* Sealiger affirms that the word inseda was applied to these 
animals, not on account of their appearance, but because they 
might be cut into or asunder without destroying life. Pliny 
adheres to the common acceptation, which is, in all probability, 
the right one. 
-f- Lacordaire's Introd. cL VEnt. I. 3 ; Audouin’s Resume 
d'Entomobgie. 
