INSECTS' HAIRB. 589 



bend near their extremity, in each of which supervenes an 

 elastic membranous expansion, and from which a very 

 minute quantity of a clear, transparent fluid is -emitted 

 when the fly is actively moving, explains its capacity for 

 clinging to polished surfaces. It simply remains to add 

 that the tubular nature of the shaft of the tenent-hairs on 

 the foot cf this insect has been surmised, although its 

 minute size and homogeneity hardly admits of actual con- 

 firmation. At the root of the pulvillus, or its under sur- 

 face, is a process, which in some instances is short and 

 thick, in others long and curved, and tapering to its ex- 

 tremity (Scatophaga), setose (Empis), plumose (Hippobos- 

 cidce), or, in '?ne remarkable example (Ephydra), so closely 

 resembling in its appearance the very rudimentary pul- 

 villus with which it is associated. Just at the base of the 

 fifth tarsal joint, on its under surface, there is present, in 

 Eristalis, a pair of short, very slightly curved hairs, which 

 point almost directly downwards. It became desirable to 

 endeavour to ascertain how far the structure of these 

 tenent-hairs agrees with that of true hairs, on which some 

 valuable critical observations were made last year by Dr. 

 Hicks. 1 



" Tenent-hairs are usually present in some modification 

 or other, that it is really difficult to name a beetle which 

 has not some form of them ; the only one I yet know that 

 seems to me really to possess nothing of the kind is a 

 species of Helops, which lives on sandy heaths ; I suppose 

 the dense cushion of hairs on the tarsi here to be for the 

 protection, simply, of the joints to which they are attached. 

 I have detected them on the tarsal joints of species of 

 Ephydra, and on the first basal tarsal joint of the Drono 

 of the Hive-bee. A very rudimentary form of tenent-hairs 

 is present on the under surface of some of the Tree-bugs 

 (Pzntatomidce), which have in addition a large, deeply-cleft 

 organ at the extremity of the tarsus, which appears to be 

 a true sucker. 



" When walking on a rough surface, the foot represents 

 ihat of a Coleopterous insect without any tenent appen- 

 dages. The ungues are always attached to the last joint of 



(1) See Trans. Linn. Soc. vol. xxiii. p. 143. 



