SYSTEM OF INSECTS. 391 
this Order have only txoo wings, yet the under or secon- 
dary wings of the other Orders have in them their re- 
presentative a . Their poisers also, I formerly observed 
to you, are probably more connected with their respira- 
tion than with their flight b . 
Def. Metamorphosis incomplete, or coarctate. 
Mouth proboscidate c . 
Prothorax replaced by a collar. Sutures of the 
trunk mostly spurious d . 
Wifigs two, with winglets attached to them : 
neuration various e . Poisers. 
Tarsi pentamerous. 
Ovipositor various f . 
11. Aphaniptera 8 {Aptera L. Lamarck. Rhyngota F. 
Suctoria Latr.) This is an osculant Order, and is dis- 
tinguished from the other Aptera L. in undergoing a 
regular metamorphosis. The larva is vermiform, the 
pupa incomplete, and inclosed in a cocoon. Probably 
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. Be- 
sides their metamorphosis, they are distinguished from 
the Aptera by the number of segments into which their 
body is divided, and by their pentamerous tarsi. Some- 
a Vol. II. p. 354—. b Ibid. p. 355. 
c Vol. III. p. 465—. d Ibid. p. 552—. 
? Ibid. p. 632. f See above, p. 163. 
b' From uQuvyis, inconspicuous ; so named because something like 
elytra appear. 
