CLASSIFICATION 



9 



Fir,. IT. 



part of entomologists has been followed by a gradual increase 

 in the number of orders, until our present system has been 

 attained. 



Owing to the incomplete condition 

 of entomological knowledge, however, 

 the best system as yet proposed is but 

 tentative and more or less open to 

 objection. The most competent and 

 widely approved classifications are 

 those of Brauer and Packard, and 

 the system here adopted is essentially 

 that of Brauer, with certain important 

 modifications made by Packard. 



In the course of the following syn- 

 opsis of the orders of insects it is 

 necessary to use some terms, as meta- 

 morphosis and thysanuriform, in an- 

 ticipation of their subsequent defini- 

 tion. 



i. Thysanura. No metamorphosis. 

 Mouth parts mandibulate, either free 

 (ectognathous) or enclosed in the 

 head (entognathous). Wings inva- 

 riably absent. Thoracic segments simple and similar. Ab- 



.dominal segments ten, 

 with two to eight pairs 

 of rudimentary limbs 

 and two or three anal 

 cerci. Eyes aggregate, 

 compound or absent. 

 Antennae multiarticulate. 

 Integument thin. Ex- 

 amples, Campodca (Fig. 

 9), Japyx, Maclrilis, 

 Lepisma (Fig. 10). Some one hundred and seventy-five spe- 

 cies are known. 



The snow flea, Acho- 



rntcs niz'icola. Length, 

 2 mm. 



Smirithurus hortensis. Length, 1.2 mm. 



