io8 STUDIES IN THE EVOLUTION OF ANIMALS 



Pigs and Tapirs are banded when young ; an imported young 

 specimen of Tapirus Bairdi was covered with white spots in longi- 

 tudinal rows, here and there forming short stripes. Even the Horse, 

 which Darwin supposes to be descended from a striped animal, is 

 often spotted, as in the dappled Horses ; and a great number show 

 a tendency to spottiness, especially on the haunches.' 



Ocelli may also be developed from spots or from bars, as 

 pointed out by Mr. Darwin. 



On p. 290, Dr. Wallace also mentions that in certain diseases 

 the pigment is destroyed along the course of a nerve and its 

 branches. 



In this connection Mr. Darwin says : l * Three accounts have 

 been published in Eastern Prussia, of white and white-spotted 

 Horses being greatly injured by eating mildewed and honeydewed 

 vetches, every spot of skin bearing white hairs becoming inflamed 

 and gangrenous.' 



Other similar cases are quoted in other animals. 



' We thus see that not only do those parts of the skin which 

 bear white hair differ in a remarkable manner from those bearing 

 hair of any other colour, but that some great constitutional difference 

 must be correlated with the colour of the hair ; for in the above 

 mentioned cases, vegetable poisons caused fever, swelling of the 

 head, as well as other symptoms, and even death, to all the white 

 or white-spotted animals.' 



Some great constitutional difference must be correlated with the 

 colour of the hair. Undoubtedly ; and the starting-point would seem 

 to be the electricity of the nerve-centre cells, corresponding to the 

 white parts of the skin, acted on electrically by the poison in the 

 blood circulating among those central cells. 



No one who has thought on this subject can doubt that the 



1 Animals and Plants under Domestication, vol. ii. p. 331, second edition. 



