DR. J. BRAXTON HICKS ON UNDESCRIBED SENSORY ORGANS IN INSECTS. 117 
abruptly, so as to give the edge in most cases the appearance of a ridge running round 
the palpus. This is well shown in Tetrix, &c, and in the Coleoptera. 
Closely resembling these tactile hairs, we find on the proboscis of Musca, Mescm brh- 
mm, and many dipterous genera, as Eristalis, &c, on the delicate under surface 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 Musca 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 difficult 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 peculiar 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-louse 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 just 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 then- usual form 
on the general integument, are to be found on those parts of the members which neces- 
sarily come into contact with bodies in the natural movements ; as, for instance, the 
pads of the tarsi, &c. That these are used as instruments of touch, some have demed ; 
still 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, corneal 
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 
rufa (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. ' , 
Finding thus that these modified hairs are situated on those parts that are usea for touch- 
ing, and that they become most modified in form in those parts that are employed more 
particularly for delicate touch, and are supplied with nerves proportionately to their altered 
form, I think we are justified in concluding that the highest form of **^Jiz. 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 ol 
the general surface possess the function of common feeling. To follow the nerve into tne 
