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XI. On a new Structure in the Antenna; of Insects. 

 By J. B. Hicks, Esq., M.D. Loud., F.L.S. 



Read June 2nd, 185/. 



The object of this paper is to call attention to some peculiar structures to be found in 

 the antennae of insects, which have not been hitherto noticed. If we submit the antennae 

 to the bleaching process which I have before described (see pp. 141-2), these structures 

 wiU be well brought into view ; they vary somewhat in form in the different genera, but 

 all, I believe, possess the same elements, and are formed on the same principle. 



I shall first describe those of the Diptera. 



The antenna of the common Blow-fly {Musca vomitoria) is usually described as consisting 

 of three joints, the terminal one being dilated and elongate, having a plumose seta or 

 bristle on one side. There are many genera of Diptera which possess a similar antenna, 

 and it is on this third dilated joint that the structures about to be described are found. 

 When the antenna is not so constructed, although many of the joints present similar 

 appearances, yet I believe they will not be found on the first and second joints, but almost 

 invariably, if not always, to commence on the third, as may be seen in the accompanying 

 figures. 



First, of the Blow-fly {Musca vomitoria) (Tab. XXIX. fig. 1). Over the whole surface 

 of the elongated third joint may be noticed at first sight, a multitude of transparent dots, 

 apparently vesicles, but on closer examination and in profile, they will be foimd to be level 

 with, if not rather below the general surface (fig. 1, 6 1). These dots after a careful inves- 

 tigation prove to be perforations of the inner coat of the waU of the antenna, closed in 

 externally by a very thin membrane, which can be seen, when the antenna is crushed, 

 on the lines of fracture. 



Behind this closed perforation is a sac, rather larger than the perforation itself, wlaich, 

 when the antenna is broken up, may be found floating about in the balsam (fig. 1, d 1). 

 The diameter of these perforations of the inner wall of the antenna is about 50^00 inch. 

 They are placed very close together. The area on each half of the antenna covered by 

 these structures, has a surface-measurement of ^ inch by -^ inch, and as each square of 

 ^ inch has within it 3025 (that is, a square having 55 on each of its sides), the total 

 number embraced within the space occupied by them will be about 9075 ; and the total 

 for both sides wiU therefore be about 18,150. But it Avill be proper to deduct from 

 this number about 1000 for the space occupied by the apertures (presently to be described), 

 and some possible irregularities in the disposition of these organs; we may therefore 

 assign 17,000 for the whole surface of each antenna. 



But besides this multitude of peculiar structures, there are niimerous apertures leading 

 into cavities, which may be either simple or composed of one to five chambers, all commu- 



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