RESPONSE TO LIGHT 115 



upon which the insects are placed. SchUeper (1927) first showed 

 by means of experiments, in which the wall of the screen was 

 lined with adjacent vertical stripes of different shades of grey and 

 of various colours, that insects do not respond to the movement 

 of the pattern if the grey and coloured stripes appear of equal 

 brightness for the eyes of the creatures (an analogous effect is 

 known in human sense physiology). By this means it was possible 

 to determine, not only the relative brightness of different coloured 

 papers, but also to discover different colours which appear of 

 equal brightness for a given insect. If the insect responds to the 

 movement of a pattern, which consists only of stripes of equal 

 brightness, but of different colour, it becomes evident that it is 

 able to differentiate colours. If under the same circumstances it 



•600 700 WO 500 -400 -300 -ZOO 100 



^ — ii Mi i li " '1^ J ^ ^ 



I ^ I I I ! ! 



Fig. 52. Approximate limits of visible spectrum for man {a-h) and 

 the bee {c-d). 



does not respond, the insect may be regarded as being colour-blind. 

 By using this method Schlegtendahl (1934) showed that several 

 beetles, including Geotrupes, the fly Fannia canalicularis, and also 

 some night-flying Noctuidae, all show evidence of colour vision. 



Little is known concerning the actual physiological nature of 

 colour vision in insects. Kuhn (1927) made the suggestion that 

 blue and yellow in the one case and blue-green and ultra-violet in 

 the other might be complementary colours. At present, however, 

 there is very little evidence available in connection with this 

 suggestion. Kuhn, however, carried out experiments wherein he 

 trained bees to visit blue surfaces and made sure that there was 

 no interfering tendency to visit the yellow. He then exposed a 

 series of square pieces of card of different shades of grey and 

 placed one single yellow card among them . Over each card was a 

 paper ring of a contrasting shade of grey. He noted that the bees 



