52 THE ZOOLOGIST. 



neutralise drift, provided the wing-power is adequate. The 

 test for the last requirement can only be the environment in its 

 widest extent. 



The argument may be led against a second component based 

 on visual impressions that the existence of an analytical 

 mechanism under the first component, and dependent on an 

 internal sense of displacements, renders the second component 

 unnecessary. The contention is justified with regard to certain 

 animals which, conditionally or otherwise, receive little or no 

 external impressions. In these animals the first component is 

 evidently very highly developed, and in itself is possibly 

 adequate to compass the return home. But in birds and many 

 insects the relatively great efficiency of the visual organs has, 

 there are reasons to believe, militated against a gradual refine- 

 ment of -the sense of displacements to a grade of efficiency 

 sufficient to control the course, which must be a " bee line " 

 to be serviceable. As much is proved by the effect of fog and 

 total darkness. These, as we have seen, destroy or disable the 

 faculty of distant orientation. They do not, however, obliterate 

 the knowledge of the position of the objective in space, for this 

 knowledge remains intact. But the means of getting there is, 

 for the time being, partially or completely lost. 



Whenever the sense of direction for one reason or another 

 fails, a return to the original point of departure is possible only 

 by a visual re-orientation on that point of departure. As much 

 is evident from some of Prof. Watson's experiments and from 

 the Canary, which, after its cage was retained in a new position 

 for some time, had to look for the door of the cage before it was 

 able to return. Evidence as to the linear distance over which 

 visual re-orientation can be accomplished is available, so far as 

 I am aware, for Pigeons only. Hachet-Souplet left Pigeons at a 

 certain place, and moved the cote to conspicuous positions at 

 increasing distances from that place. When the separation 

 amounted to more than ten or twelve kilometres, the Pigeons 

 failed to return home.* It is thus evident that the appearance 

 of the home, or original point of departure, is intimately associ- 

 ated with its position in space ; and that, when the two are 



* VI. Congres Internat. de Psychologie, p. 663, 1910. 



