DR. J. BRAXTON HICKS ON UNDESCRIBED SENSORY ORGANS IN INSECTS. 143 



the depth of which varies extremely — from a mere depression, as in the Lacquey-moth 

 (Clisiocampa Neustria), to a tube extending inwards to half, or more, of the length of the 

 joint. Sometimes the tube is of the same diameter throughout, or even dilated at the 

 innermost end. What the nature of the inner surface of this tubular depression is, it is 

 very difB.cult to ascertain from its position. It certainly possesses numerous hairs, and 

 apparently there are some circular markings between them at the deepest part. How^ 

 ever, upon one point there is no doubt, viz. that a nerve proceeds distinctly to it alone, 

 and spreads out upon the apex of tliis cavity (PI. XIX. fig. C, 1 5, 2 6). It is held in its 

 position by two or three bands which are attached to the interior of the wall of the palpus. 

 The aperture of this structure when tubular (which is its most frequent form) is shown 

 at fig. C, 1 a, 2 a. I have given figures of it in Argynnis Paj)hia and in a Geometer- 

 moth. In a large number of different species examined, I have never found this struc- 

 ture absent. 



In Aclierontia Atropos (Death's-head Moth) there is no depression, the part being merely 

 marked by a circular yeUow spot. 



I have found something similar to this in the first joint of the palpus in Bibio Hard 

 (Diptera), which I have drawn at PI. XIX. fig. D, 1. There are about twenty- four 

 irregularly-shaped hollow cells or compartments on the floor of the cavity, each of which 

 is divided from its neighbom-s by a rather stout septum; and a number of hairs 

 spring up from the floor of each cell, and from the sides of the walls dividing them 

 (See PL XIX. fig. D, 2). I have not as yet met with this condition in any other 

 dipterous insect. 



I shall now pass to a class of structures quite dissimilar to those already mentioned. 

 They are to be found on the palpi and those parts about the mouth whose function is 

 that of touch, as the apex of the palpi, proboscis of Lepidoptera and of Diptera, and also on 

 the apex of the antennae, being peculiar modifications of true hairs, and not processes of 

 the cuticle. It is requisite to bear in mind the true nature of the hair in Insects, — 

 namely, that it is situated in a depression caused by the absence of the inner layers of the 

 integument, into which the cuticle is continued. In the centre of this cuticular depression 

 a small elevation or papilla arises, which is the true root of the hair, and which rises from 

 it of various length. By means of this arrangement, the hair itself is capable of some 

 degree of motion. The interior of the root of each hair is in connexion with the 

 internal parts of the member on which it is situated ; commonly fibres run to it, probably 

 always including a branch of a nerve ; and this is decidedly the case in those hairs sitiiated 

 near the prominent parts and extremities of the various members, as, for instance, the tips 

 of the antennae, the palpi, pads of tarsi, &c. ; and this branch of the nerve does not run into 

 the interior of the hair, but only to the inner aspect of the root, which separates it entirely 

 from the interior. The difference between this structure (true hairs) and cuticular pro- 

 cesses must be particularly borne in mind : the latter, having no root, and not being situated 

 in a depression, evidently only spring from the surface. The spine must also be distinctly 

 separated from the true hau', being a tapering process of the whole integument, into the 

 interior of which the contents of the body can freely pass. 



The palpi have been considered by most naturalists as the organs of touch, both from 



