THE PLAY OF ANIMALS. 235 



passion they perform strange antics or rapid nights, as 

 much probably from the internal impulse to motion 

 and exertion as with any desire to please their mates." * 



The act of singing, too, which was originally a means 

 of recognition, " is evidently a pleasurable one, and it 

 probably serves as an outlet for superabundant nerv- 

 ous energy and excitement, just as dancing, singing, 

 and field sports do with us.".f 



These are the essentials of Wallace's theory. Se- 

 lection through the female is excluded; at the most he 

 thinks we may say that she prefers the " most vigour- 

 ous, defiant, and mettlesome male/' and so indirectly 

 favours the ornamentation which results from abundant 

 energy. 



In this presentation of Wallace's theory I have 

 maintained a careful distinction which is not made 

 clear in his own works, but without which it is difficult, 

 in my opinion, to understand thoroughly the meaning of 

 his ideas. I mean the distinction between the biological 

 principles that would refer our problem to the familiar 

 operations of natural selection, and such physiological 

 theories as those of Tylor and Spencer. The former 

 are of the greatest value, and will lead, I believe, to im- 

 portant modifications of the Darwinian system, while 

 in the latter there is no inherent vitality, though Wal- 

 lace seems to lay great stress on them. 



Turning now to the secondary aspect of this theory, 

 we set out from the fact that the characteristic marks 

 and appendages of animals are closely connected with 

 their anatomical structure, just as, in a common disease, 

 an eruption occurs on the forehead which corresponds 

 exactly to the distribution of the ophthalmic division of 



* Ibid., pp. 294 and 287. f Ibid., p. 284. 



