364 Annals Entomological Society of America [Vol. IX, 



haunts, they swim about with a zigzagging, jerky motion, 

 against the hurrying currents, maintaining their relative 

 positions and even surmounting the stream with little effort. 

 Their ability to cope with a rapid flow is readily appreciated 

 by a consideration of the structure of their legs. The anterior 

 pair are more or less simple, as usual, and so is the posterior. 

 Their function not having been directly observed, it can only 

 be surmised that they do not differ from the other Veliidce. 

 The middle legs, however, are worthy of all attention. In 

 these, the femora are more or less swollen in both sexes, greatly 

 so in the males, not so much in the females. The tibiae are 

 long and slender, and the tarsi taken together are nearly as 

 long as the tibiae. These tarsi are highly specialized, and in 

 them lies the secret of Khagovelias ability to breast strong 

 currents. The last tarsal joint is split for about half its length, 

 and in the split, at its base, is set a plume-like arrangement, 

 which may sometimes be noticed projecting from the tarsus in 

 dried museum specimens. A little mild speculation was excited 

 by this plume, and Champion, in Biologia Centrali Americana, 

 suggested that it might be spread fanwise on the surface of 

 the water. Very fortunately a direct observation of this 

 plume in use happened to be made and it was published, so its 

 function is now well understood. In swimming, the tarsus 

 of Rhagovelia lies on the surface along its entire length, with 

 the split perpendicular to the surface. The plume, which is 

 made up of a number of feather-like hairs fastened at one end 

 at the base of the slit and free at the other, is now opened 

 downward into the water, where it spreads fanwise, thus acting 

 in a somewhat similar manner to the web foot of a fowl or the 

 fin of a fish. Of course, this gives the insect a comparatively 

 tremendous purchase and enables it to successfully propel 

 itself against a strong flow. 



A few general considerations now suggest themselves. It 

 would seem from the facts set forth that any insects provided 

 with such highly specialized devices fitting them to cope with 

 a complex environment can scarcely be considered primitive 

 forms, not if evolution be operative as is commonly asserted 

 and with simple scientific faith believed to be. Whatever 

 structures are seemingly simple can be explained by the fact 

 of disuse or by non-specialization due to unspecialized use. 



