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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 Rhagavelia obesa, and copies of his drawings will be 

 found on plate'Viii; 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 efiiciency in swimming. The middle tibiae 

 possess tibial combs like the littoral forms. Unlike their 

 more specialized relatives, they walk very well upon the land. 



The Nepidse also present little modification of the limbs for 

 traversing the water, due no doubt to their "lying in wait" 

 habits. The Belostomatidae have their second and third pair 

 of limbs flattened and fringed with hairs. Bueno says that 

 "Lethocerus amer-icanus when hard pressed and with a free 



