DR. J. BRAXTON HICKS ON UNDESCRIBED SENSORY ORGANS IN INSECTS. 149 
are also ; and this view is certainly strengthened by the fact that the respiratory organs 
and their accompanying nerves are distributed 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 Coleoptera, a hard spine-like membrane, then a fluid, thirdly, through 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 thus 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 nervure 
of the wings, base of halteres, and elytra, I have already expressed my opinion in the 
Journal of the Linnean Society (I. 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 base of the wings, which are so frequently in 
motion and so near the large thoracic spiracle, through which the air is continually 
pas sin 
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 air is the only medium by 
