140 DE. J. B. HICKS ON A NEW ORGAN IN INSECTS. 



the commencement of the air-passages in the upper animals, pro- 

 bably because the current of air or water passing the olfactory 

 nerves is there most powerful ; but in the spiracle-breathing in- 

 sect the greatest currents are in the neighbourhood of the wing, 

 and near the greatest thoracic spiracle. The motion of the hal- 

 teres also permits a greater exposure to odours floating in the air. 



That the olfactory nerves should be necessarily, and by analogy, 

 always before the optic, will not hold good below Fishes, where 

 they first appear in that position. Otherwise the auditory appa- 

 ratus in Crustacea ought to be behind the optic. In fact, there 

 is no known analogy on this point, as no olfactory organs have yet 

 been described below Vertebrata. Besides, if there are no nerves in 

 front of the optic except those to the mouth and antennae, either 

 these latter must be olfactory organs, or the olfactory organs must 

 be sought for elsewhere behind. 



It may be added, that the respiratory apparatus is diffused (as 

 are the nervous centres), and not connected with the oral or nasal 

 aperture ; and although the sensations be the same, analogy forms 

 no sort of argument that the organs of sensation should always 

 occupy precisely the same place. 



Description of Plate V. 



Fig. 1. Nervous system of the Drone-fly (Fristalis tenax) : a, nerve of first 

 leg ; b } nerve of second leg ; <?, nerve of third leg ; d, nerve of wing ; 

 e, nerve of one of the halteres. 



Fig. 2. Nervous system of Blow-fly (Musca vomitoria) ; nerves lettered as 

 above. 



Fig. 3. Details of Rhingia rostrata ; 3 a, base of one of the halteres : a, group 

 of vesicles on ridge ; b, ditto on the broad facet ; b\ a group of larger 

 vesicles on the side of b. 3 b, base of one of the halteres, another view, 

 showing, «', group of vesicles on the other ridge ; 3 c, magnified vesi- 

 cles of the ridge, diameter 4000th of an inch ; 3 d, ditto on broad 

 facet, diameter 3700th of an inch ; 3 e, profile of 3 c. 



Fig. 4. Details of the largest Crane-fly (Tipula oleracea ?) : 4 a, base of one of 

 the halteres ; 4 b, ditto, another view ; 4 c, several of the vesicles on 

 the ridge, diameter 1900th of an inch ; 4 d } ditto on broad face, dia- 

 meter 3000th of an inch ; 4 e, ditto on the conical lobe at the junction 

 of the halteres with the body. 



Fig. 5. Details of Blow-fly (Musca vomitoria) : 5 a, base of one of the halteres ; 

 5 i, another view of ditto ; 5 c, vesicles on the ridge, diameter 2720th 

 of an inch ; 5 d, ditto on the broad facet with the small lateral group, 

 diameter 3730th of an inch. 



Fig. 6. Details of Bee (Andrena Mouffetella) : 6 a, dorsal view of the vesicles 

 on the costa of the hind wing ; 6 i, section of ditto. 



Fig. 7 a, Subcostal nervure of the Ermine Moth, upper side ; 7 b, section of 

 ditto. 



Fig. 8 a, Base of anterior wing of Leptis scolopacea, showing the base of the 

 subcostal nervure on the upper side ; 8 b t ditto on the under side. 



