178 COLOUR IN NATURE chap. 



that is, two molecules of the orange pigment might 

 combine, and form one molecule of red and one of 

 yellow pigment. The chief interest of this suggestion 

 lies in the fact that such a splitting of colours has 

 been described in the males as compared with the 

 females in both birds and butterflies. It may quite 

 well be that this is in reality due in some such way 

 to a chemical change. In butterflies, as ,we have 

 already seen, there is certainly a strong tendency for 

 colours like yellow, orange, and red to show oscillation 

 in amount. 



Into the numerous other problems connected 

 with the colours of insects space does not permit us 

 to enter here. Many of them are indeed subjects 

 which can only be adequately treated , by ento- 

 mologists, and reference should be made to the works 

 of Wallace, Poulton, Weismann, Meldola, Beddard, 

 and others for details. It is, however, hoped that 

 the foregoing summary will be of use in calling 

 attention to aspects of the subject which are less 

 familiar, but are undoubtedly of great importance. 



The Colours of Spiders 



Among other Arthropods the colours of spiders 

 merit at least a brief notice. In them the pigments 

 do not seem to have been investigated at all, and 

 the structural colours only to a very slight degree, 

 but there are some interesting observations on the 

 colours themselves. 



As compared with insects, the characteristics of 

 spiders which are important for our purpose are the 

 practical absence of obvious~^egmentation in the 



