44 ANTS AND SOME OTHER INSECTS. 



trail, to perceive what is to the right, left, behind or before her, 

 and consequently what direction she is to take, according to whether 

 she is bound for home, or in the opposite direction to a tree in- 

 fested with Aphides, or the like. 



Singularly enough, I had established this latter fact in my 

 "Etudes Myrme'cologiques en 1886" {Annales de la Societt Ento- 

 mologique de Belgique} before I had arrived at its theoretical inter- 

 pretation. But I was at once led by this discovery in the same 

 work to the interpretation just given. Without knowing of my 

 work in this connection, A. Bethe has recently established (dis- 

 covered, as he supposes) this same fact, and has designated it as 

 "polarisation of the ant-trail." He regards this as the expression 

 of a mysterious, inexplicable force, or polarisation. As we have 

 seen, the matter is not only no enigma, but on the contrary, a nec- 

 essary psychological postulate. We should rather find the absence 

 of this faculty incomprehensible. 



But everything I have just said presupposes a receptive brain. 

 The formation of lasting perceptions and associations cannot take 

 place without an organ capable of fixing the sense-impressions and 

 of combining them among themselves. Experience shows that the 

 immediate sensory centers are inadequate to the performance of 

 this task. Though undoubtedly receptive, they are, nevertheless, 

 incapable of utilising what has been received in the development 

 of more complex instincts and can turn it to account only in the 

 grosser, simpler reflexes and automatisms. To be sure, a male 

 ant has better eyes than a worker ant, and probably quite as good 

 antennae, but he is unable to remember what he has seen and is 

 especially incapable of associating it in the form of a trail-image, 

 because he is almost devoid of a brain. For this reason he is un- 

 able to find his way back to the nest. On the other hand, it is well 

 known that the brain of a man who has lost a limb or whose hear- 

 ing is defective, will enable him to paint pictures with his foot, 

 write with the stump of an arm or construct grand combinations 

 from the images of defective senses. 



I venture, therefore, to designate as topochemical the olfactory 

 antennal sense of honey-bees, humble-bees, wasps, etc. 



