SENSATION AND REACTION 91 



an attraction to insects that visit the blossoms to obtain 

 nectar, and the doubts that some subsequent observers have 

 thrown on the existence of a true colour sense in insects do 

 not seem to be justified. An experiment of J. Lubbock 

 (1882) often quoted, and several times subsequently verified, 

 is especially valuable in this connection. He placed honey 

 on a coloured paper disc and thus trained bees to associate 

 a particular colour (red or blue, for example) v^ith the 

 location of food ; then he found that a bee which had once 

 found honey on a blue disc would return to a disc of that 

 colour even though the food were now not on a blue but 

 on a red one. This experiment shows that in such cases 

 the attraction by colour must be more powerful than the 

 attraction by scent, and confirmation has been afforded by 

 Forel and others who, having varnished or removed the 

 feelers of various insects, found that reaction to the colour 

 stimulus remained unaflFected. 



We may conclude, therefore, that the eyes of many insects 

 enable the creatures to distinguish the forms and colours 

 of near objects ; Eltringham estimates that butterflies 

 recognise members of their own species when about a yard 

 away. Those with large compound eyes can see in many 

 directions at once. Beyond the restricted distance for 

 which the lenses and cones of its eyes afford suitable focus, 

 an insect can appreciate changes in the intensity of the light 

 falling on its corneal area. Any one who passes his hand 

 above the station of a resting fly can demonstrate that an 

 insect perceives a moving shadow, readily if the motion 

 be rapid, less distinctly if it be slow. If the observer is 

 trying to catch the fly with his moving hand, he may go 

 farther in his interpretation of the insect's behaviour, and 

 conclude that the approaching shadow " startles " or 

 " frightens " it when he sees it dart suddenly away. 



This reference to the possible sensations or mental 

 experiences of insects recalls the opening remarks of this 

 chapter on an insect's response to stimulation from a source 

 of light, and the inferences that may be drawn from the 

 creature's behaviour. It may be advisable to return to such 



