128 THE COLOURS OF ANIMALS 



Determination of the part affected by surrounding 

 colours 



Having thus defined the time of susceptibility, the 

 next question was to ascertain the organ or part of 

 the larva which is sensitive. At first it appeared 

 likely that the larvae might be influenced through their 

 eyes (ocelli), of which they have six on each side of the 

 head. Hence in many experiments the eyes of some 

 of the larvae were covered with an innocuous opaque 

 black varnish, and they, together with an equal number 

 of normal larvae from the same company, were placed 

 in gilt or white surroundings. The pupae from both 

 sets of larvae were, however, always equally light- 

 coloured. It then seemed possible, although highly 

 improbable, that the varnish itself might act as a 

 stimulus similar to that caused by white or gilt 

 surroundings, and therefore the experiment was re- 

 peated with black surroundings in darkness ; but the 

 pupae of the two sets were again almost identical, so 

 that it appeared certain that the eyes can have 

 nothing to do with the influence. 



It then seemed possible that the large branching 

 bristles, with which the larvae are covered, might con- 

 tain some organ which was affected by surround- 

 ing colours, but experiments in which half of the 

 larvae were deprived of their bristles showed con- 

 clusively that the sensitive organs must have some 



