CLASSIFICATION ' 7 



Owing to the incomplete condition of entomological knowledge, how- 

 ever, the best system as yet proposed is but tentative and more or less 

 open to objection. The most competent and widely approved classifica- 

 tions 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 synopsis of the orders of insects it is 

 necessary to use some terms, as metamorphosis and thysanuriform, in 

 anticipation of their subsequent definition. 



i. Thysanura. No metamorphosis. Mouth parts mandibulate, 

 either free (ectognathous) or enclosed in the head (entognathous). 



FIG. 9. Campodea. Length, 3 mm. 



FIG. 10. Lepisma. Length, 10 mm. 



Wings invariably 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. Examples, Campodea (Fig. 

 9), Japyx, Machilis, Lepisma (Fig. 10). Some one hundred and seventy- 

 five species are known. 



2. Collembola. No metamorphosis. Mouth parts entognathous 

 and typically mandibulate, with occasional secondary suctorial modifica- 

 tions. Wings invariably absent. Thoracic segments simple and similar 



