588 PSYCHICAL FACULTIES OF ANTS AND OTHER INSECTS. 



The vision of the retinal eye is especiall}- directed to the detection 

 of movements — i. e., to the relative local changes in the retinal picture. 

 In flight it localizes large space areas, but defines contours of objects 

 lesf^ sharply than our eve does. The retinal eye gives but a single 

 upright image (P^xner), whose clearness increases with the number of 

 facets and the convexity of the eye. Exner succeeded in photo- 

 graphing this image in Lamj>yris. The inmiobility of the eyes neces- 

 sarilv makes it impossible for an insect at rest to see stationary objects 

 situated laterally from it. This is the reason why insects at rest are 

 so easily caught by slow movements. In light, insects orient them- 

 selves in space ])y means of the retinal eyes. B3' the displacement of 

 pigment many insects can adapt their eyes for use by day or by night. 

 Ants perceive the ultra-violet rays with their eyes. Bees and beetles 

 distinguish colors, though indeed not as the same tints that we do, 

 since they arfe not attracted to those flowers that seem to us most 

 l)eautiful. Perhaps this comes from some mixture with the ultra-violet 

 rays not perceived l)y us. 



The ocelH play a subordinate part and apparently serve only for 

 near vision in dark ])laces. 



The olfactory sense resides in the antennse, especially in their club- 

 like ends — that is to say, their ])()i"e plates and olfactory bulbs. Being- 

 movable and externally situated upon the antennal tips, they impart to 

 the insect at least two attributes wanting to verte))rates and especially 

 to man: 



{<() The ability to recognize the chemical qualities of an object b^^ 

 means of direct contact (tactual smell). 



(/>) The abilit}' to recognize and distinguish, by means of odor, the 

 shape and extent of an object, including also the form of its own 

 track, and in this way to establish associated memories. 



The olfactory sense of many insects gives, therefore, definite and 

 clear relations of known space, and may serve very well to orient ani- 

 mals that move about on the ground. I have on that account named 

 this qualitative sense, quite differing from our smell in its specific 

 energy, topochemical olfaction. Apparently the pore plates serve to 

 detect odors at a distance and the olfactoiy l)ull)s for tactual smell, 

 3'et this is only supposition. The removal of the antennse destroys 

 the power of distinguishing friend from foe and deprives the ant of 

 the abilit}'^ to orient itself on the ground or to find its way, while 

 three legs and an antenna may be removed without essentially injuring 

 these functions. The topochemical sense enables the ant to distinguish 

 from each other the two directions of its trail, an ability which Bethe 

 considers to be due to a mysterious polarization. 



The organ of taste is found in the mouth parts. The taste reactions 

 of the insect are very similar to our own. Will, having accustomed 

 wasps to seek honey at a definite place, then put quinine in it. The 



