46 ANTS AND SOME OTHER INSECTS. 



Even in many insects with movable antennae and of less aerial 

 habits, e. g., the chafers and bombycid moths, the antennal olfac- 

 tory sense is evidently much better adapted to function at a dis- 

 tance, i. e., to the perception of odors from distant objects, than 

 to the perception of space and trails. Such insects find their way 

 by means of their eyes, but fly in the direction whence their an- 

 tennae perceive an odor that is being sought. 



A genuine topochemical antennal sense is, therefore, probably 

 best developed in all arthropods, whose antennae are not only mov- 

 able in the atmosphere, but adapted to feeling of objects. In these 

 cases the still imperfect topochemical oder-sense for distances can 

 be momentarily controlled by the contact-odor-sense and defini- 

 tively fixed topographically, i. e., topochemically, as we see so ex- 

 tensively practised in the ants. 



It would be possible to meet this view with the objection that 

 a contact-odor sense could not accomplish much more than the 

 tactile sense. I have made this objection to myself. But in the 

 first place it is necessary to reckon with the facts. Now it is a fact 

 that insects in touching objects with their antennae mainly perceive 

 and distinguish the chemical constitution of the objects touched 

 and heed these very much more than they do the mechanical im- 

 pacts also perceived at the same time. Secondly, the tactile sense 

 gives only resistance and through this, form. On the other hand, 

 the multiplicity of odors is enormous, and it is possible to demon- 

 strate, as I have done for the ants, and Von Buttel-Reepen for the 

 bees, that these animals in distinguishing their different nest-mates 

 and t'heir enemies, betray nothing beyond the perception of ex- 

 tremely delicate and numerous gradations in the qualities of odors. 



In combination with topochemical space-perception, these 

 numerous odor-qualities must constitute a spatial sense which is 

 vastly superior to the tactile sense. The whole biology of the so- 

 cial Hymenoptera furnishes the objective proof of this assertion. 



It would certainly be well worth while to investigate this mat- 

 ter in other groups of arthropods which possess complex instincts. 



In conclusion I will cite an example, which I have myself ob- 



