SYSTEM OF INSECTS. 383 
the common flea and the chigoe would form distinct 
genera. The number of species of fleas is greater 
than has been supposed. I have been informed that 
Dr. Leach is acquainted with fourteen British species 
alone. Besides their metamorphosis, they are distin- 
guished from the Aptera by the number of segments into 
which their body is divided, and by their pentamerous 
tarsi. Something like elytra and a scutellum appear to 
distinguish these insects. 
Der. Metamorphosis incomplete. 
Body apterous, compressed. 
Mouth rostrulate*. 
Tarsi pentamerous. 
We are now come to those insects which, though they 
change their skin in their progress to their state of per- 
fection, and some of them, as we have seen?, gain addi- 
tional segments and pairs of legs, yet none of them ac- 
quire wings or wing-cases: these I have considered as 
forming one Order, under the denomination of 
12. Aprera‘’ (Synistata, Antliata, Unogata, Mito- 
sata F.). I do not give this as a natural Order. Our 
knowledge, however, of the internal organization of its 
groups, is not at present sufficiently matured to warrant 
the formation of them into new Classes‘: till that is more 
fully ascertained, it seems to me therefore better to con- 
sider these groups as forming three Suborders: the first 
consisting of the Hexapods ; the second of the Octopods ; 
and the third of the Polypods. It will be better, I think, 
* Vou. III. p. 471. > Tbid. p. 23. 
© From a, privative, and x7egop. “ Vor. Ill. p. 22—. 
