BEHAVIOR OF ANTS AND MYRMECOPHILES 403 



of direction. The return after going out from the nest is ex- 

 plained by assuming that the sensorium of the ant receives a 

 sensation of direction on the outward trip. This sensation is 

 received at the beginning of the trip and maintained through- 

 out its course, for no matter how many times the ant deviates 

 from the general direction it returns each time. This phenom- 

 enon Cornetz calls "the constant reappearance of the once 

 impressed wandering direction." This direction memory of 

 the trail may be of greater complexity. When ants had 

 become accustomed to a pile of grain at a certain point, the 

 grain was removed some distance. The ants diverged from the 

 old spot, found the grain and returned to the point at which 

 they had left the outgoing trail, and then went directly to the 

 nest. Here a memory of two separate directions is shown. 

 The secondary trails, diverging from the principal outgoing 

 trail, were at right angles to it. 



Cornetz concludes from these observations that sight, smell, 

 touch, chemotropism and topochemism play no role in the 

 return of a solitary foraging or hunting ant, but that it is guided 

 by an impression received by the sensorium at the beginning of 

 the outward trip. From the fact that the outward trail is sinu- 

 ous while the homeward is more direct, it is evident that the 

 ant does not possess a kinometric muscular memory. Touch, 

 smell and sight are probably valuable in guiding the ants in 

 the immediate vicinity of the nest, where they lose the earlier 

 impression of direction. But after a heavy rain, that had lasted 

 two days and changed completely the general surroundings of 

 the nest, the ants went out and returned as readily as before, 

 when they had been familiar with the immediate vicinity of 

 the opening. 



Cornetz (9) reviews Santschi's paper " Observations et Re- 

 marques Critiques sur le Mecanisme de 1' Orientation chez les 

 Fourmis, " in which the effect of the sun's rays was said to be 

 an important factor in orientation. This phenomenon Cornetz 

 calls the "solar tropism of Santschi." He considers that it 

 helps greatly in explaining the constancy of orientation, but 

 doubts its application to ants moving about in the deep woods, 

 or in the shade in general, unless we assume that certain as 

 yet unknown rays of the sun penetrate through walls, trees, 

 etc., not being absorbed by these bodies. When the sun was 



