40 THE UNIVERSITY SCIENCE BULLETIN. 
limbs covered with a close pile, and the last two have the claws 
still terminal upon the tarsi. This series leads to the Gerrids 
and Veliids, which habitually traverse the open water. With 
these the bodies are set with a covering of short close pile and 
the limbs are long, distributing the weight over a greater sur- 
face. The claws are small and subapical, thus affording less 
likelihood of the limb piercing the surface film. Bueno has 
figured the remarkable modification of the foot of the middle 
leg of Rhag govelia obesa, and copies of his drawings will be 
found on plate! VGA, figure 6. The last tarsal segment is deeply 
cleft and furnished with a series of ciliated hairs capable of 
spreading into a fan-like structure. According to Bueno, this 
fan-like structure spreading from beneath the cleft in the tar- 
sus projects into the water and aids the insect in rowing. 
Rhagovelia is found in the swiftest part of the streams, and 
this unique device is a material aid to its locomotion. This 
bug has the reputation of diving and swimming under water. 
This habit, however, does not indicate that in any such a way 
the true aquatics came to extend their range. More probably 
did it come about by the occasional submergence of some 
Gelastocorid-like form frequenting the margins of streams and 
tidal marshes, and clinging tenaciously to its haunts, though 
occasionally and even periodically submerged. Masen, in 
Entomologist’s Monthly Magazine, vol. XXV, p. 236, cites two 
species of Saldids that move about from plant to plant under 
water. 
Thus we come to the true aquatics. Mr. Bueno gives some 
observations on the methods employed by the various forms in 
a paper entitled “Ways of Progression in Water-bugs.”’ 
It will be apparent to any who examine the true aquatic 
Heteroptera that, among them, the Naucorids represent the 
latest addition to the water fauna. The hind limbs are spiny 
and angular, like the Gelastocorids, and possess few, if any, 
hairs that make for efficiency in swimming. The middle tibize 
possess tibial combs like the littoral forms. Unlike their 
more specialized relatives, they walk very well upon the land. 
The Nepide also present little modification of the limbs for 
traversing the water, due no doubt to their “lying in wait” 
habits. The Belostomatide have their second and third pair 
of limbs flattened and fringed with hairs. Bueno says that 
“Lethocerus americanus when hard pressed and with a free 
