388 DR. J. B. HICKS ON THE ORGANS 



In some of the Lamellicorns the closing-in membrane is prolonged to a point, sometimes 

 rigid, so as to be easily mistaken for a hair ; but closer inspection and comparison, I am 

 sure, will satisfy any one as to its trvic nature. I can best explain what I mean, by the 

 antenna of Geotritpes stercorarius. The surface of the lamellae is patterned all over in 

 the same parts as in the former Lamellicorns, and in a very similar manner to those of 

 Andrena fulva, shoA\aa in fig. 8 of my former paper. The surface is occupied with about an 

 equal number of true hairs, and articulated projections very like hairs (I. fig. 2 b), beneath 

 each of wliich is a sac, as in the former kind of antennae ; and as the sac does not extend 

 through the whole thickness of the antenna-wall, there is, as in Dynastes, a tubular com- 

 munication Math the interior of the lamella. (See I. figs. 1, 2.) 



This structure will help to explain other forms in the Lamellicorn groups, as for 

 instance in the Stag Beetle {Lucanus Cervus). Over the same parts as in the others 

 are a number of apparent hairs, slightly curved, projecting from the antenna-wall. On 

 looking more closely, it will be observed that they are not all true hairs ; on the contrary, 

 only a few of the larger ones are hairs, while beneath the rest an elongated sac is placed, 

 as is shown at K. figs. 1, 2. In this insect the terminal lamella has a large cavity — 

 sometimes there are two — extending deeply into its interior (fig. 3). The diameter of the 

 sac is axoo inch. 



A similar condition exists in Hydrophilus piceus ; but the nature of the sacs is well shown 

 by the fact that some have the closing-in membrane level, and others slightly raised, whilst 

 some have it prolonged into a spine (G. fig. 2). The diameters range from y^g-o to 

 3^,-00 inch. This peculiar-shaped antenna has nine joints ; the last three are liberally 

 furnished with these sacs, and of a larger size than any I have hitherto found : possibly 

 the size of the insect will account for it, though it may generally be said that the size of 

 the insect has but slight relation to the size of the sacs, as will be seen by comparing 

 the various measm'ements I have given. 



That these sacs with hair-like apices are the same as those which are found in Melolontha, 

 Dynastes, &c. is evident from the facts — 1st, that they are situated in the sarqe position ; 

 2nd, that some have level, others spinous apices on the same antenna ; 3rd, so far as I have 

 found on examination of a large number of insects, I think it may be laid down as a rule, 

 that no cuticular projection or spine has a cavity or sac beneath it in any other part of the 

 insect, except in the antennae. In some Hemiptera I have foxind beneath the true hairs a 

 cavity, but not like these sacs, inasmuch as the whole antenna-wall was protruded, with a 

 true hair at the apex. 



The spinous condition of the covering-in membrane is an important point, because it 

 seems to be clearly at variance with what is generally understood to be the structure of 

 an olfactory organ. Again, when we consider the habit of HydropMlus and compare it 

 with another aquatic Beetle, Dyticus muryinalis (to be presently alluded to), I think we 

 may obtain a clue as to the nature of these organs in the antennae. If watched atten- 

 tively, it will be seen that the HydropMlus is very careful not to wet his antennae. The 

 moment he is placed in water he suddenly brings them beneath the joint of the head and 

 thorax, where they remain in a hollow, sm'rounded by the silvery film of air which covers 

 the under surface of the thorax, and which is collected by the numerous downy hairs on 



