148 DR. J. B. HICKS ON A NEW STRUCTURE 



nicating with the common aperture. These apertures are protected slightly hy hairs which 

 arise from the edges, and also a little way within them (fig. 1, b2,c,d2). There are ahout 

 eighty of these cavities on one side of the antenna, and probably about the same number on 

 the other ; their diameter varies from sotoo to x^ao' inch. The largest sacculated chamber 

 is about 6^0 inch. By focusing down to the floor of this cavity, papillse may be seen, each 

 in the centre of an hexagonal area. On viewing these structures in profile, as at fig. 1, d, 

 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 waUs of the chambers. This is shown at 

 fig. 2, d 2. 



In Selophilm pendulus (Tab. XXIX. fig. 2), the smaller organs first described are not 

 so numerous as in Miisca 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, d 2. 



In many antennae 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- 

 hrywm merklianum. 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 antennae of this form, varying in relative 

 numbers in the different genera. 



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-jouited, 

 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 wiU 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 Tabamis (Tab. XXIX. fig. 3) the third joint is much dilated, but unequally, so that 

 the four other joints, although contiaued 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 

 tWo to 3 0^0 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 Jjombyllv.s 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 -g-vVo to 33^00 inch. 



In Hippobosca equina, the antenna is 5-jointed ; the third, fourth and iifth 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 



