68 INTRODUCTION TO 



which it is derived, is exactly synonymous with the 

 Greek one svropct,, 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 antennae ; 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 



* Scaliger affirms that the word insecta 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. 



t Lacordaire's Introd. a VEnt. I. 3 ; Audouin's Resume 

 (TEntoniologie. 



