DR. J. BRAXTON HICKS ON UNDESCRIBED SENSORY ORGANS IN INSECTS. 149 



are also ; and tliis view is certainly strengthened by the fact that the respiratory organs 

 and their accompanying nerves are distriljuted in a diffused manner throughout the 

 whole length of the Insect's limbs, instead of being concentrated anterior to the ex- 

 tremities, as in the Vertebrata. Reasoning from analogy, therefore, will clearly not hold 

 in this case ; indeed there can be little doubt (and this view is held by some of our best 

 naturalists) that the true homological relations of the various organs in the Vertebrata 

 and Invertebrata are to be decided rather by the analogy of their form, structure, and 

 evident functions, than by that of their position. 



These circumstances should guide us in determining the functions of the structures I 

 have now brought under notice; but at present I think it would be premature to 

 attempt finally to assign a particular function to any of these organs, excepting those 

 of the antennae, which I have described on two former occasions ; still I may venture to 

 throw out a few hints for further investigation in the matter. 



That there is every reason to think that the antennal organs are those of hearing, 

 I have stated in my papers above mentioned ; at all events I do not think it possible to 

 suppose they can be olfactory organs, according to our present ideas of the essentials of 

 that organ. It is difficult to understand how odorous particles can pass through, as in 

 some Coleoi)tera, a hard spine-like membrane, then a fluid, thirdly, througli a thin mem- 

 brane to reach the extremity of the nerve, while a wave of sound can readily be con- 

 ceived to be capable of tlius impressing upon the nerve the required impulse. The non- 

 existence of an otolith within these sacs cannot, I think, be considered as conclusive 

 against their being auditory organs, — and for this reason, that as every Invertebrate 

 hitherto described as having an auditory organ is aquatic, so it does not seem a necessary 

 consequence that, should an air-breathing Invertebrate be discovered to have an auditory 

 apparatus, such structure requires an otolith. The conditions of the transmission of 

 the waves of sound are totally altered, and it is possible that the multitudinous repetition 

 of these organs on the antennae in some Insects may preclude the necessity of such an 

 addition within the auditory sac. 



Regarding the function of the organs so liberally supplied with nerves on the ncrvure 

 of the wings, base of halter es, and elytra, I have already expressed my opinion in the 

 Journal of the Linnean Society [l. c. p. 139) : namely, as in the Vertebrata we find 

 the olfactory organ near the respiratory aperture, so that, by the process of breathing, 

 a constant supply of fresh odorous particles can be brought to it, we may, I think, 

 expect from analogy to find, in those animals where the position of the respiratory organ 

 is altered, that the olfactory sense will accompany it : and I may ask, where should we 

 find it more suitably placed than at the l)ase of the wings, which are so frequently in 

 motion and so near the large thoracic spiracle, through which the air is continually 

 passing. 



I think we may reasonably conclude that the organs I have above described on the 

 palpi in Diptera and Hymenoptera are in some measure connected with the sense of taste, 

 being situated around the mouth, perhaps supplemental to other organs ; and one can 

 scarcely deny a similar function to the tube running inwards from the apex of the palpi 

 in Lepidoptera. That they are in a position where the aii- is the only medium by 



