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



probably the external layer of the antennal wall continued over it ; and this is perhaps 

 the condition in every variety of these structures (fig. 6, a 2). 



In fig. 7 is represented the antenna of Eucera longicornis ; the whole surface is occupied 

 by a number of saucer-like depressions, which are arranged so close that they touch each 

 other on all sides. In the centre of these is clearly seen the tubular perforation of the 

 internal wall, closed in by the very thin membrane. The diameter of the perforation 

 is about ttVo i^ich ; the whole saucer-like depression is y-iVo inch. If a fi'acture be made 

 in the antenna, the above thin membrane will become detached and float about in the 

 balsam. Beneath the perforation will be found, by very careful examination, a membra- 

 nous sac (ilg. 7, c). These sacs touch each other all round, the whole forming a thick 

 layer on the internal surface of the wall of the antenna. The number of these structures 

 in this insect is about 2000 for each of the ten joints furnished with them ; the total will 

 therefore be about 20,000. 



In fig. 8 is shown the antenna of another Hymenopterous insect {Andrena fulva). 

 It has the same construction as the last-mentioned, except that there are hairs between 

 the saucer-like depressions ; and each hair as weU as the depressions being surrounded 

 by a ring of very minute tubercles, the whole has a pretty appearance. 



In the Ichneumons which I have examined, I find the appearance different, though the 

 real structm-e is not so. The perforation remains the same, but the thin transparent 

 membrane closing it in, is elevated above the general surface, and extends lengthwise 

 lieyond the perforation, while it is generally not so wide. The shape of this membrane 

 is not unb'ke that of an inverted canoe, and a keel-Uke ridge extending longitudinally 

 through its centre adds to the similitude. The perforation beneath it is oval. I have 

 endeavoured to show this at fig. 9, a, b, c. 



The extreme length of the external arched membrane I have found in one specimen to 

 be g-j^ inch; the longest diameter of the subjacent perforation is TTro> the shortest 

 aroo inch. 



The antenna of Vespa vulgaris and of V. crabro is arranged on the same principle, but 

 the organs are more numerous and not quite so regularly disposed. They are well 

 shown in the pupa state. 



In Nomada the appearance is much the same as in Apis mellijica. 



But the most beautiful of all the structures I have as yet met with is that presented in 

 the antenna oi Idbellula depressa (Tab. XXX. fig. 10). This antenna has six joints. The 

 thii'd, fourth and fifth have on one side the following organs. 1st, a simple, nearly round 

 sac, formed in the internal membrane and projecting inwards ; the external opening 

 being closed in by the delicate thin membrane, as noticed in the other insects (fig. 10, a 

 & b 2). 2nd, a sac as above, but opening inwardly into another convoluted membranous 

 sac, which is shown at fig. 10, b 1. These are more simple towards the upper joints ; and 

 in some of the simpler sacs there seems to be a small cavity at the back. Whether there 

 be any membrane separating the outer and inner sac, it is diflicult to say ; but I fancy there 

 is no separation of the kind. 



The nerve may be distinctly seen to pass to these structures, and as the cuticle has 

 scarcely any marking, the whole is plainly visible, and forms a very interesting object. 



