3 so LIGHT AND THE BEHAVIOR OF ORGANISMS 



about twice as far from the edge of the violet as the further 

 edge of the bright thaUine band " (1895, pp. 203-205). 

 Considering the results of all these different experi- 

 ments, Lubbock concluded (p. 199) " that: (i) ants have the 

 power of distinguishing colours; (2) that they are very 

 sensitive to violet; and it would also seem (3) that their 

 sensations of colour must be very different from those 

 produced upon us." We shall discuss these conclusions 

 later. 



Many experiments with various color and intensity con- 

 ditions were performed, in which the light in one part of 

 the nest was passed through carbon bisulphide so as to 

 eliminate the ultra-violet. It was found in general that, 

 other conditions being equal, the ants avoid the light con- 

 taining ultra-violet rays. These rays, although invisible 

 to man, appear therefore to stimulate the ants somewhat 

 like the rays which are visible. These results agree with 

 those of Lubbock on Daphnia and those of Graber on the 

 earthworm, and ten different species of insects as well 

 as a few other forms. It is also well known that para- 

 mecia and various bacteria can be stimulated by ultra- 

 violet. Stimulation by these rays therefore appears to be 

 fairly common among animals. 



Lubbock assumes that ultra-violet as well as the visible 

 rays in the spectrum produces color sensation in ants. 

 He says (1895, p. 220): " These experiments seem to me 

 very interesting. They appear to prove that ants per- 

 ceive the ultra-violet rays. Now, as every ray of homo- 

 geneous light which we can perceive at all appears to us 

 as a distinct colour, it becomes probable that these 

 ultra-violet rays must make themselves apparent to the 

 ants as a distinct and separate colour (of which we can 

 form no idea), but as unlike the rest as red is from yellow, 

 or green from violet." 



Very few will agree with Lubbock in assuming that he 

 has demonstrated color vision — subjective sensation in 

 ants. His results however are reliable. There can be no 



