290 DARWINISM chap. 



as the animal grows older; then the stripes expand, and 

 at last, meeting together, the adult animal becomes of a 

 uniform dark brown colour. So many of the species of 

 deer are spotted when young, that Darwin concludes the 

 ancestral form, from Avhich all deer are derived, must have 

 been spotted. Pigs and tapirs are banded or spotted Avlien 

 young ; an imported young specimen of Tapirus Bairdi 

 was covered with white spots in longitudinal rows, here 

 and there forming short stripes.^ Even the horse, Avhich 

 Darwin sup2Doses to be descended from a striped animal, 

 is often spotted, as in dappled horses ; and great numbers 

 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. Spots are an ordinary form of 

 marking in disease, and these spots sometimes run together, 



I forming blotches. There is evidence that colour markings are 

 in some Avay de2)endent on nerve distribution. In the disease 



' known as frontal herpes, an eruption occurs which corresponds 

 exactly to the distribution of the ophthalmic division of the 

 fifth cranial nerve, mapping out all its little branches even 

 to the one Avhich goes to the tip of the nose. In a Hindoo 

 suffering from herpes the pigment was destroyed in the arm 

 along the course of the ulnar nerve, with its branches along 

 both sides of one finger and the half of another. In the leg 

 the sciatic and scaphenous nerves Avere partly mapped out, 

 giving to the patient the appearance of an anatomical 

 diagram.'^ 



These facts are very interesting, because they help to 

 exjjlain the general dei^endence of marking on structure which 

 has been already pointed out. For, as the nerves everywhere 

 follow the muscles, and these are attached to the various bones, 

 we see how it happens, that the tracts in which distinct 

 developments of colour appear, should so often he marked out 

 liy the chief divisions of the bony structure in A^ertebrates, and 

 by the segments in the annulosa. There is, however, another 

 correspondence of even greater interest and imi^ortance. 



[ Brilliant colours usually a])pear just in proportion to the 



^ See coloured Fig. in Proc. Zool. Hoc, 1871, p. 626. 

 - A. Tylor's Coloration, p. 40 ; and Photograph in Hutchinson's Illustra- 

 tions of Clinical Surgery, quoted by Tylor. 



