XXVIII 



ground color of the upper surface of the wings of Danais Plexippus consists 

 of all the red and yellow of the spectrum and about 75^/0 of the green". 

 Here we have to do, therefore, with a butterfly of the same genus Danais, 

 with which we were concerned just now and which is also closely allied to the 

 genus EuPLOEA. 



On the one side we have, therefore, a number of very careful observations 

 which, on being correlated, completely elucidate and confirm each other, by 

 means of which a number of biological phenomena are explained, hitherto not 

 to be accounted for in any other way, and for whose interpretation all sorts 

 of unproved and even incomprehensible influences have been invoked. On the 

 other side we find some incomplete anatomical investigations, some technical 

 dexterity in which certainly cannot be denied, but whose relevance in this 

 connection is very doubtful and which were, moreover, accompanied by so litde 

 knowledge of what had already been proved by investigation and comparison in 

 this field, that this must of necessity have exercised great influence on the 

 interpretation of the results of these investigations. I believe the choice between 

 these two cannot admit of much doubt. 



I think the foregoing observations are sufficient to convince the unprejudiced 

 that the theory of colour evolution rests on a firm basis and can in no way 

 be considered as refuted. I will not further dilate on this; those desiring further 

 information on this subject and as to what is to be observed in this connection 

 in other animals may find additional particulars in the chapter " Farbeuevohttioti " 

 in the second section of my work " AMi einmal Mi7nicyy, Sclcktion, Danviiiistnus " 

 published in 1907. I would only here quote the following from the treatise 

 published in 1 904 by Dr. Arnold Jacobi " Dt'e Bedeutung der Farben im Thier- 

 reich ". " The first pigments " this savant states "to arise, in the gradual develop- 

 ment of animals, appear to be those corresponding to the left side of the 

 rainbow and admitting, therefore, only rays of very great wave-length and very 

 little refrangibility and as a consequence red is the most common ground colour 

 to which yellow is gradually and green sometimes also added. That red is 

 the starting point of all colour development may be inferred from the fact that 

 the actual perception of light in our eye is connected with a finely divided 

 red substance, Rhodopsin, in the retina. Thus the primitive eye-spots in various 

 Infusoria are red and in Turbelaria and Chaetopoda, living in great depths 

 of water where light scarcely penetrates, as in the subterranean Aphides, the 

 eyes are also red, although the pigment in the eyes of their allies exposed to 

 light is dark. 



Moreover, many animals whose stage of development has retained an ancient 

 simple character are red, such as, for instance, some lobsters; even our common 



