DR. J. BRAXTON HICKS ON UNDESCRIBED SENSORY ORGANS IN INSECTS. 147 



abruptly, so as to giye the edge in most cases the appearance of a ridge running round 

 the palpus. This is well shown in Tetrix, fee, and in the Coleoptera. 



Closely resembling these tactile hairs, we find on the proboscis of Ilusca, Ilesembri- 

 num, and many dipterous genera, as EnstaUs, &c., on the delicate u.nder siu-face of that 

 suctorial organ, some nipple-like bodies, which apparently are hairs in origin (PL XIX. 

 fig. T, 3), but which are, with their follicles, much firmer than the membrane from which 

 they spring ; in Mnsca vomitoria and domestica they are well-marked, as in PL XIX. 

 fig. T, 1 ; while in Eristalis, &c. the hair itself is much abbreviated, although the integu- 

 mental tube is long, lying obliquely in the membrane (PL XIX. fig. T, 2). Their minute- 

 ness renders it difiicult to ascertain whether a branch of the nerve proceed to them ; but, 

 from their position on the under surface, which is that used for touching, it is probable 

 that such is the case. And as the proboscis of the Diptera is certainly in part used for 

 the same purposes as the palpi in other insects, it seems also highly probable that these 

 bodies have a similar function, particularly when we consider that the palpi of the 

 Diptera are generally devoid of those pecxdiar hairs which I have called " tactile;" 



Now these "tactile hairs" are found not only in Insecta, but also in Myriapoda and 

 Arachnida, and probably in all the Articulata. In the common Wood-loixse the apex of 

 the feeler is depressed, from the centre of which spring three shortened hairs, the tips of 

 which appear only just above the edge of the depression. In the Grass-tick {Ixodes) there 

 are two cup-shaped depressions close together near the end of the fore leg, from the 

 centre of which three or four hairs arise, whose apices extend jvist beyond the level of 

 the margin. These I have shown at PL XIX. fig. U. 



While considering the relation of these hairs to the sense of touch, it seems proper here 

 to mention that on other parts of insects also, hairs, much altered from their usual form 

 on the general integument, are to be found on those parts of the members which neces- 

 sarily come into contact with bodies iu the natural movements; as, for instance, the 

 pads of the tarsi, &c. That these are used as instruments of touch, some have denied ; 

 stUl I am sure that careful investigation would lead to the conclusion that such is their 

 vocation. On examining the tarsal pads, we shall find that they have shortened, conical 

 and delicate hairs, sometimes closely crowded, as in the Wood- Ant (PL XVIII. fig. M, 3) ; 

 sometimes sparingly so, as in the Tetrix. To these hairs I have observed in every case a 

 nerve proceeding, giving off branches to their roots. This is well marked in Formica 

 rnfa (Wood- Ant). (PL XVIII. fig. M, 3, a.) 



As the pads on the last joint of the tarsus of the Diptera have been closely investigated 

 by others, I have not pursued their anatomy. 



rinding thus that these modified hairs are situated on those parts that are used for touch- 

 ing, and that they become most modified in form in those parts that are employed more 

 particularly for delicate touch, and are supjDlied with nerves proportionately to their altered 

 form, I think we are justified in concluding that the highest form of feeling, viz. touch, 

 resides in them, especially in those of such extreme delicacy as are found on the terminal 

 membrane of the palpi, while those on the pads of the tarsus, &c. we may suppose 

 to possess the sense of touch also, but in a less degree,— and further, that the hairs of 

 the general surface possess the function of common feeling. To follow the nerve into the 



u2 



