378 DR. HICKS ON THE KERVE AT THE BASE OF THE HALTERES, AND ON 



This can be well observed in Bhingia rostrata and Eristalis tenax. (See figure.) 



The nerve in the subcostal nervure is disposed in a somewhat similar manner. But in 

 many instances I have found the ganglionic enlargement to possess more than one 

 nucleus ; two or three apparently coexist in the Coleoptera (see a, figs. 4, 5, 6). The 

 distal end of this enlargement tapers off to a rather fine extremity, so that it may pass up 

 through the canals which pierce the integumental layers. 



The mode of termination in these nerves points out a homology to the termination of 

 the optic nerve, as seen in its development in insects, and is, indeed, probably the method 

 by which all nerves of sensation end, as has been shown by M. N. Jacubovitsch in the 

 Comptes Hendiis, May 7, 1860, p. 859. (See ' Microscopical Journal,' April 1861.) 



In some — the Saw-flies for example — the ganglionic enlargement is not elongated, but 

 applied immediately beneath the canals ; so that, crowding as they do together, the whole 

 seems as a compact layer of ganglionic cells. 



The outer nerve-sheath is attached to the edge of the skin-canal, as is shown in figs. 4, 

 5 & 6, reminding one of the condition of the nerve-sheath of the compound eyes by which 

 it attaches itself to the facetted cornea. 



We are indebted to Leydig for the additional knowledge of the ganglionic enlargement 

 at the termination of the nerve supplying these structures *. Upon reviewing my papers, 

 he states also that he has found little conical "pegs or rods" (" Stifte, Stabchen") with 

 their bases towards the integument, which are situated in the extremity of the nerve, one 

 or two in each. These, I must confess, after a very careful search through numerous 

 specimens (many being the same as those inv.'hich he describes them), I have been unable 

 to discover, and am therefore under the impression that he has fallen into some error — 

 the more so as he admits that it was only after a dozen trials that he himself succeeded. 

 It is a difficult thing to prove a negative ; but, though I have frequently traced the nerve 

 to its very end, I have failed to distinguish any such structures as the " Stifte " or " Stab- 

 chen," either in specimens just killed or kept in spirit for different periods. I suspect 

 that the method which he adopts of pulling out the nerve, by withdrawing the organized 

 layer lining the integument internally and which passes within and lines the tube 

 (skin-canal), has possibly led to the appearances described by him. I have noticed in 

 the larger beetles a condition which renders this highly probable. Be this as it may, 

 there can be no hesitation in assigning, as I have already done, an important sensory 

 function to the organs taken as a whole. 



Leydig is under the impression that they are of the same nature as the organ in the 

 hinder part of the thorax in the Acridce, &c. first pointed out ])y Miiller, Avhich he con- 

 siders an organ of hearing. That they may be homologous to those in the Acrida, would 

 seem to derive some confirmation from the circumstance that he has not found Miiller's 

 organ in the same part in other insects, while I have not found those I have pointed out 

 on the wings of the Orthoptera. 



But are they, therefore, auditory organs ? Have they any similarity to \vhat we know 

 of this organ in the Invertebrata ? I confess my inability to see any resemblance beyond 



* Eeichert unci Du Bois-Reymond's Archiv, 18G0, No. 3, p. 299. 



