MR. TUFFEN WEST ON THE FOOT OF THE FLY. 401 



possible source of error. The influence tliey have had in the formation of opinion since 

 the date of their publication is the best test possible of the esteem in which they are 

 held. And, in addition, the merit may fairly be claimed for them, of having stimulated 

 other inquirers to a closer examination of the questions under consideration, 



E. Newman (1841)* speaks, from independent observations, of the "almost infinite 

 number of minute hairs" composing "the soft cushions ov jndvilli, on the under sm-face 

 of the joints of the tarsus," in insects generally, which, at their ends are slightly dilated, 

 and constantly exude an adhesive gummy matter. By means of these gummy i^HZei^Zi, 

 " insects possessing them are enabled to walk freely on smooth surfaces, even with their 



backs downwards, against the power of gravity." 



"Until lately discovered by Mr. Lister," it is added, " the true cause " by which they are 

 enabled to do this "was unknown." 



Kirby and Spence do not appear to have used the compound microscope in their 

 investigations into the minute structures of insects. In the earlier editions of their great 

 work they seem to have been guided in the formation of their opinions by the weight 

 they attached to Home's authority, and subsequently by Mr. Blaekwall's latest published 

 observations. Mr, Kirby makes some valuable observations on the action of the parts 

 composing the Ply's feet, as deduced from the habits of the insects, both when in what 

 we may term the natural condition of the foot, and when it is defiled by the insect's 

 attempting to walk on a surface slightly moistened by the breath, or coated with flour, 

 or when the same material was powdered over them. 



It is added " that these observations on the way in which flies are able to support 

 themselves against gravity cannot be considered as wholly settling the question as to the 

 precise way in which these pulvilli and those of insects generally act in eifecting a similar 

 mode of progression ; and my main reason for here giving these slight hints is the hope of 

 directing the attention of entomological and microscopical observers to a field, evidently 

 as yet so imperfectly explored." 



Under date " July 11th, 18-12," Kirby adds an observation of considerable interest. 

 Shortly after writing the remarks above quoted, he observed a "fly on the window, 

 whose motions seemed very strange. I approached it," he says, "and found that it was 

 making \dolent contortions, as though every leg was affected with St. Vitus's dance, in 

 order to pull its pulvilli from the surface of the glass, to which they adhered so strongly 

 that though it could drag them a little way, or sometimes by a violent effort get first one 

 and then another detached, yet the moment they were placed on the glass again they 

 adhered as if their under side were smeared with bird-lime. Once it succeeded in dragging 

 off its two fore-legs, when it immediately began to rub the pulvilli against the tarsal 

 brushes ; but on replacing them on the glass, they adhered as closely as before, and it 

 was only by efforts almost convulsive, and which seemed to threaten to puU off its limbs 

 from its body, that it could succeed in moving a quarter of an inch at a time. After 

 watching it with much interest for five minutes, it at last by continued exertions got its 

 feet released and flew away, and alighted on a curtain, on which it walked quite briskly, 



* Entom. Mag. Tol. i. p. 447. Grammar of Entomology, a Familiar Introduction to the History of Insects. 



