HETEROPTERA. — HYDROMETRID&. 469 
considering the full-grown size of these wingless individuals, adopted 
the opinion that they were species distinct from such as acquired 
wings, as the winged and apterous specimens of Velia*, &c. It appears 
to me, however, that, from causes of which we are ignorant, numerous 
individuals of many of-the species of these tribes are subjected to an 
inferior kind of development in the imago state, which does not allow 
the acquirement of wings ; which, however, in certain cases, acquire 
their full size. Hence, the same principle must be applied to the 
completely apterous individuals of Velia or Hydrometra as to the 
half-winged individuals of Pyrrhocoris apterus or Prostemma guttula, 
which no one regards otherwise than as specifically identical with the 
full-winged specimens of the same species. Hence, I consider that 
the apterous specimens of Hydrometra stagnorum, those with very 
short elytra (as figured in the Crochard ed. R. An. pl. 92. f. 6.), and 
those with full-sized wings and wing-covers (Curtis, pl. 32. fig. sup., 
and my jig. 120. 6.+), are all in the imago state, although some are 
more perfect than others. Another circumstance confirming this 
opinion is the ordinary condition of the pupa state of such individuals 
as acquire wings: whereas the pupa state of the ultimately wingless 
specimens is necessarily destitute of rudimental wing-cases ; hence 
we cannot consider these wingless insects as stopped in their develop- 
ment, or, in other words, as imagines, left enveloped in the skin of the 
pupa {, but must be compelled to regard them as imagines with pe- 
culiar characters of their own, somewhat analogous to the neuters, or 
undeveloped females of the bees; but yet more perfect than that 
kind of imago, being capable of reproduction.§ 
The very young larva of Gerris || differs materially from the adult 
specimens in form, being very much shorter and broader, the hind 
legs appearing inserted near the extremity of the body, owing to the 
* See Mag. Nat. Hist. 1st series, No. 18., on V. rivulorum and V. currens, 
regarded as distinct species. 
+ Scopoli’s other species having the “ abdomen lineis elevatis longitudinaliter 
striatum ” is probably a full-winged specimen, the longitudinal veins of the wings 
being mistaken for abdominal ridges. 
¢+ Hence the inutility of Mr. Curtis’s suggestion to cover a number of the 
wingless Velie with a gauze covering, in order to see whether they would not ulti- 
mately obtain wings. i 
§ In my memoir on these insects, in the Annales de la Soc. Entomol. de France, 
I have entered more fully into this question. 
|| Gilbert White (Nat. Hist. Selborne,) believed these insects to be viviparous. 
HH 3 
