ANTS AND SOME OTHER INSECTS. 17 



tween the directions of its trail, a faculty which Bethe attributes to 

 a mysterious polarisation. The ability to sense different odors 

 varies enormously in different insects. An object possessing odor 

 for one species is often odorless for other species (and for ourselves) 

 and vice versa. 



The gustatory organs are situated on the mouth-parts. Among 

 insects the reactions of this sense are very similar to our own. Will 

 accustomed some wasps to look in a particular place for honey, 

 which he afterwards mixed with quinine. The wasps detected the 

 substance at once, made gestures of disgust, and never returned to 

 the honey. Mixing the honey with alum had the same result. At 

 first they returned, but after the disagreeable gustatory experience 

 they failed to reappear. Incidentally this is also a proof of their 

 gustatory memory and of their powers of association. 



Several organs have been found and described as auditory. 

 But after their removal the supposed reaction to sounds persists. 

 This would seem to indicate that a deceptive resemblance to hear- 

 ing may be produced by the perception of delicate vibrations 

 through the tactile sense (Duges). 



The tactile sense is everywhere represented by tactile hairs 

 and papillae. It reacts more especially to delicate tremors of the 

 atmosphere or soil. Certain arthropods, especially the spiders, 

 orient themselves mainly by means of this sense. 



It may be demonstrated that insects, according to the species 

 and conditions of life, use their different senses in combination for 

 purposes of orienting themselves and for perceiving the external 

 world. Many species lack eyes and hence also the sense of sight. 

 In others, again, the olfactory sense is obtuse ; certain other forms 

 lack the contact-odor sense (e. g., most Diptera). 



It has been shown that the superb powers of orientation ex- 

 hibited by certain aerial animals, like birds (carrier-pigeons), bees, 

 etc., depend on vision and its memories. Movement in the air 

 gives this sense enormous and manifold values. The semi-circular 

 canals of the auditory organ are an apparatus of equilibrium in 

 vertebrates and mediate sensations o.f acceleration and rotation 

 (Mach-Breuer), but do not give external orientation. For the dem- 



