LIGHT AND MOVEMENT 



food, in spite of an immense load between their mandibles and in face 

 of all obstacles, has excited admiration and conjecture for centuries. 

 Nevertheless, although considerable intelligence is suggested, the 

 response is largely automatic. Cornetz (1911) observed that if such an 

 insect were lifted up and set down in another place, it set off in the same 

 direction as before whether or not this led to the nest. That the 

 directing influence was the sun was shown by Santschi (1911) who 

 shaded the ant from the sun and deflected its rays by a mirror so that 

 they reached the insect from the opposite side ; each time this was 

 done the ant immediately changed its path so that it maintained the 

 same direction with regard to the reflected rays as it had previously to 



69 



5^9'pnn 



2^ 39'pnn. 



Fig. 44. — Menotaxis. 



The orientation of the ant, Lasius niger. The dark Une indicates the 

 route taken by the ant towards its nest, N. The initial part of its journey 

 was orientated at an angle of about 90^ to the sun. At X, the ant was 

 imprisoned in a box for 2.V hours, from 2.39 p.m. to 5.9 p.m. During this 

 time the sun had traversed an angle of 37-5°. On its release, the ant resumed 

 its path again at right angles to the late afternoon sun, deviating from its 

 former path by an angle of 37° (after Brun). 



the direct rays (Fig. 43). The same reaction was demonstrated in 

 locusts by Kennedy (1945-51), who found that the direction of the 

 marching desert hoppers could readily be changed and that of flying 

 adults momentarily changed by reflecting sunlight onto them with a 

 mirror. At first this response was assumed to be a typical examjDle of 

 the light-compass reaction, but Wellington (1955) broitght forward 

 evidence that it was more probable that radiant heat associated with 

 the reflected light was the more effective stimulus. 



A still more elaborate response was demonstrated in the classical 

 experiment of Brun (1914) who confined an ant in a box for some hours 

 in the middle of its homeward journey to its nest ; on releasing the 

 insect it set out on a new track, not now towards its nest but deviating 

 from its original route by an angle corresponding to that through 

 which the sun had moved in the interval so that its rays were still 

 received at the same angle as before (Fig. 44). Again, this was initially 



