OTHER THEOEIES OF SEXUAL COLOURING 323 



appendages is due to a surplus of vitality, and may be 

 connected with the vivacity and excitability of the 

 males in the breeding season. He also accepts Mr. 

 Alfred Tylor's theory that colours and patterns are 

 developed in relation to underlying organs and struc- 

 tures. It is convenient to discuss these two views 

 together, for they have much in common. 



Mr. Tylor argued that the modification of pattern 

 in the different regions of the body of such an animal 

 as the zebra, is related to the changes in the various 

 parts of the skeleton which are concealed beneath the 

 surface ; he even believed that the black marks on the 

 heads of tigers, &c., are related to the chief convolu- 

 tions on the surface of the brain beneath. 



It is quite possible to understand why the pattern 

 should change in the different regions of the animal 

 body, because of the greater protective value or higher 

 aesthetic effect of such an arrangement, so that if 

 Sexual Selection be accepted Mr. Tylor's theory be- 

 comes unnecessary. Furthermore, it is difficult to see 

 why such an inert, although important, structure as 

 the skeleton should so greatly affect the appearance of 

 an animal. Why should not the liver, with its vast 

 blood-supply and manifold functions, produce some 

 of the effects believed to be wrought by one of the 

 most passive tissues in the body ? Or if the muscles 

 and nerves which follow the skeleton are supposed to 

 be the efficient cause, rather than the bones them- 

 selves, it must be pointed out that the structure of 



