PSYCHOLOGY. 51 



from say the sun, and such direct rays must impinge on one 

 particular point of the sensitive surface ; the consequent sensation 

 setting a particular nerve to work. 



By so moving as to keep the light in the same direction, it is 

 possible to use the latter as a sort of compass to steer by ; and 

 that the ant really does this is borne out by experiments with a 

 mirror (deflect the rays and you upset the insect's steering ! Re- 

 store the rays, and it can go ahead again !) 



4. Differences in the lighting of various parts of the sky, and 

 also of large distant or near spaces and objects, restrictions of the 

 horizon by hills, walls, trees and the like, may all affect the ant's 

 " optics," and through them its whole nervous system and move- 

 ments thereby originated. 



5. X-rays, electric conditions of the atmosphere, etc. etc., may 

 be more or less perceived without any hypothetical special sense 

 for receiving them. Air-movements may be transmitted by sensi- 

 tive hairs, and become stimuli to movement in some particular 

 direction. 



6. Of course many movements of ants are results of actual sight, 

 smell, and the like. 



Brun has written a very long and learned paper on " ant- 

 orientation " ; it is full of very many technical and rather unwieldy 

 terms, and I find the language (both as regards his German and his 

 meaning) somewhat difficult to follow. He appears in the main to 

 agree with Santschi, and he rejects all hypotheses of a special sense 

 possessed by ants only. If it is possible to state his views in a few 

 words, they appear to be something of this sort : Ant-orientation 

 is only a special case of " Orientation " in general, viz. a power 

 possessed in some degree by all living protoplasm of maintaining 

 (Static) or altering (Dynamic) the position in space of the whole 

 organism or any of its parts. 



Static orientation being a matter of mechanical forces simply, 

 e.g. the weight of the organism, the cohesion of its molecules, and 

 so forth. In Dynamic orientation the organism has power to 

 " orient " movement towards some particular object. If this 

 object is actually present to some sense (e.g. sight or smell) the 

 orientation is direct : if not it is indirect, and in this case, which 

 includes most of the more remarkable movements of ants, it is 

 prompted by memory of past sensation or some sort of inference 

 from present sensation (e.g. fatigue may tell an ant, returning to 

 the nest, " I have expended so much energy on the journey and 

 must be nearing home by this time.") Direct orientation will not 

 explain all movements of ants, as we know that some of their 

 senses are unequal to this, but indirect orientation probably will 

 explain them, without any theory of a special sense. The extent 

 to which any organism possesses the power of indirect orientation 

 depends on its development generally, and more especially on that 



