CLASSIFICATION OF INSECTS. 47 



we think, that they can obtain clearer ideas of the re- 

 lations of the different orders than by following older 

 although apparently less comphcated classifications. 



The Insects when compared with the Worms, Crus- 

 tacea, Myriopods (Centipedes and Millepedes\ and 

 Arachnids (Spiders, Scorpions, etc.) possess a body 

 in which the three regions are strongly accented or 

 differentiated. The head, the thorax, or middle 

 region, and the abdomen are, with rare exceptions, 

 distinct from each other in all adult forms. The 

 head is especially well furnished with organs, has only 

 one pair of antennae, and is defined by a constric- 

 tion, forming, as a rule, a functional neck. The 

 differentiation of the thorax from the abdomen is, 

 however, not so complete. One finds, for example, in 

 the locust that the first segment of the abdomen may 

 be, and has been by some authors, considered to be a 

 part of the thorax, and a transferrence of this first ring 

 of the abdomen to the thorax actually does take place 

 in the Hymenoptera. 



It is now admitted by many entomologists that 

 Campodea, a genus of Thysanura, more nearly repre- 

 sents the primitive wingless form from which all 

 insects may be supposed to have been derived, than 

 any other now living. Geologic evidence, which 

 would confirm this important conclusion, is as yet 

 wanting;^ but, on the other hand, as has been pointed 



1 Brongniart has chronicled the discovery of a fossil in the 

 Carboniferous supposed to be a Thysanuran allied to Lepisma 

 or Machilis. Unfortunately the information is as yet too meagre 

 to be convincing. Bull. Entom. Soc. de France, 1885, p. loi. 



