HETEROPTERA.— NOTONECTIDE. 459 
mandibles, the latter of which are armed at the sides with twelve fine 
recurved teeth: jig. 119. 5. represents one of the mandibles entire, 
and the base of the other, and of the two maxilla ; fig. 119. 6. shows 
the extremity of the mandible more strongly magnified. These organs 
are introduced into the labium, through an orifice on the upper side 
of the basal joint, represented in fig. 119. 4., which is ordinarily covered 
by the upper lip (fig.119.3.). (These figures of the mouth of No- 
tonecta are copied from original drawings made by R. Templeton, 
Esq.) 
The name of the typical genus, Notonecta, alludes to the singular 
habit which these insects have of swimming on their backs, various pe- 
culiarities in their organisation being in harmony with this peculiarity, 
as pointed out by Dufour ; such as the inclined position of the head 
towards the breast, the form of the eyes enabling the insect to see 
both above and below, &c. When stationary at the surface of water, 
as is much their custom in still hot weather, they very quickly obtain 
intelligence of the approach of danger; when, by a single stroke of 
their long paddles, which are ordinarily kept. stretched at full length, 
as represented in fig. 119. 1., they descend into the water out of sight. 
Their motions are very quick in their own element, but on the ground 
they are scarcely able to walk. They are able to fly well, their hind 
wings being exceedingly delicate. 
The larvae and pupe differ only from the imago in their smaller 
size, and in wanting wings; in the pupe the rudiments of these organs 
are enclosed in the small flat tubercles on the back: they have the same 
habits as the imago. Frisch (tom. vi. tab. 13.), De Geer, and Rosel 
have illustrated the preparatory states of these insects: according to 
the last named author, the eggs (which are attached to the stems and 
leaves of aquatic plants, and are of an oval form) are hatched in fifteen 
days; the young make their appearance at the beginning of the 
spring, and the parent survives until they have arrived at maturity. 
The genus Ploa is remarkably distinguished by the elytra being 
entirely coriaceous, and uniting together by a straight suture, not 
overlapping each other in the least. 
The genus Corixa is distinguished by several peculiar characters ; 
the prothorax being advanced behind over the scutellum: the body is 
flattened above. The three pairs of legs are all-differently organised, 
the fore legs being imperfectly prehensile, the tibia being short, and 
the tarsi composed of a single large and ciliated joint (fig. 119. 9.). 
