148 DR. J. B. HICKS ON A NEW STRUCTURE 
nicating with the common aperture. These apertures are protected slightly by hairs which 
arise from the edges, and also a little way within them (fig. 1,62,0,d 2). There are about 
eighty of these cavities on one side of the antenna, and probably about the same number on 
the other; their diameter varies from 3555 to 1250 inch. The largest sacculated chamber 
is about gl; inch. By focusing down to the floor of this cavity, papillæ may be seen, each 
in the centre of an hexagonal area. On viewing these structures in profile, as at fig. 1, d, a 
there may be seen beyond, and adherent on all sides to their walls, a firm granulated 
mass of considerable thickness, and which appears to be tubulated nearest the walls of 
the sac. This latter investigation is attended with some difficulty, and requires much 
care, but I think I am not far wrong in stating that the hexagonal areas correspond 
to the tubes which extend inwards from the walls of the chambers. This is shown at 
fig. 2, d 2. | 
In Helophilus pendulus (Tab. XXIX. fig. 2), the smaller organs first described are not 
so numerous as in Musca vomitoria, while the cavities are more frequent, though less 
chambered. . Hairs also arise from the interior of the cavity, as is shown at fig. 2, d2. — 
In many antennæ of this shape, there are one or two openings very much larger than 
the rest, in the lower part opposite the origin of the seta; these are well shown in Mesem- 
bryum meridianum. They possess the same structure as the cavities before described. 
These cavities, and their chambers or sacculi, will, I think, be found to consist of the same 
elements as the smaller organs; the chambers being compounded of groups of these, and 
seeming to be formed by the infolding of the external surface, as is shown by the presence 
of hairs inside them. > 
The above structures I have found in all antennæ of this form, varying in relative 
numbers in the different genera. i 
Before I take leave of this form of antenna, I would throw out a suggestion with 
regard to its true structure. The seta or bristle (Tab. XXIX. figs. 1 & 2) is 3-jointed, 
the last one plumose or not, as the case may be. Now it seems to me that these are the 
last three joints of a 6-jointed antenna, the third joint of which is more or less dilated on 
one side, thereby throwing aside the last three. This I think will be seen to be the true 
explanation of the seta, when it is considered what peculiar and important structures are 
developed on the third joint, which is probably dilated for their reception. | 
. In Tabanus (Tab. XXIX. fig. 3) the third joint is much dilated, but unequally, so that 
the four other joints, although continued in the general direction of the antenna, are on 
one side of the axis. On all the five joints from the third to the apex, organs are found 
exactly like the smaller closed perforations in the Blow-fly, their diameter varying from 
. 060 t0 zooo inch. Between each is a tooth-like projection of the cuticle, like a hair. 
The largest are scanty, and chiefly found on the lower part of the third joint. 
In Bombylius the antenna is 5-jointed, the third joint only possessing these closed 
perforations, and being much elongated and slightly dilated; the diameter of the pores — 
varies from 3757 to 3357 inch. : 
In Hippobosca equina, the antenna is 5-jointed; the third, fourth and fifth joints being 
devoted to the reception of the same structures, They are depressed beneath the general 
surface, in the form of a saucer, at the bottom of which is seen the thin membrane across 
