HUNGERFORD: AQUATIC HEMIPTERA. 41 
field, stretches out its raptorial front legs before it, and gives 
long strong, propulsive strokes with the other two pairs, 
moved sychronously. When not pressed they paddle slowly, 
alternating the middle and hind legs.” 
Of the Notonectidz the little Plea, living midst the tangles 
of pond vegetation, makes but short excursions from stem to 
stem by “short little clipping strokes” of its limbs. These 
limbs on superficial examination appear but slightly fringed 
with hair, but careful study will reveal them about as delin- 
eated in figure 2, plate XXWM. All their limbs end in strong 
claws. The other genera, Notonecta and Buenoa, have hind 
limbs obviously set apart for rowing. They are flattened and 
bordered with close rows of long hairs. These collapse on the 
return, spreading with the pressure of the pulling stroke. The 
tarsal claws of the hind limb are so small that they are scarcely 
discernible amidst the fringe of swimming hairs. These rear 
limbs, the height of efficiency for propulsion in the water, 
are suffered to be dragged upon the land, the other limbs 
already ungainly in their modification for prehension, afford- 
ing it an awkward means of getting about. 
The greatest diversity of limb structure is undoubtedly 
possessed by the Corixids. The middle limbs are long, lean 
structures, ending in long, slightly incurved claws. These 
are employed only in grappling the irregularities of the bottom 
of the pool, thus holding their owner to their accustomed 
foraging grounds. The hind limbs fashioned like those of 
the back-swimmers, are even quicker in their execution. In- 
deed no water insect has greater agility and darting propensi- 
ties than has the water boatmen. 
PREHENSION. 
Kirkaldy once stated that “all of the water forms (with the 
possible exception of Corixide) are raptorial.” He later modi- 
fied this to except the Hydrometra, the front legs of which are 
not thickened, stating that “although doubtless they are em- 
ployed for holding the food during feeding, they cannot be 
said to be noticeably modified for raptorial purposes.” In 
fact, the writer has found that Hydrometra habitually spears 
its prey from beneath the surface film, and retains it by 
means of the tremendously long, flexible mandibular stylets 
which are strongly and retrorsely barbed at their tip. (See 
plate X XIX, fig. 3.) 
