310 Proceedings of the Royal Iriah Academy. 



summer than in winter ; and, further, the fat of an animal should be 

 more deeply coloured in winter than in summer. It is obvious that 

 these experimental proofs of my theory cannot be performed all at 

 once. But I do not care to delay publication until I can myself 

 institute the necessary investigations, since some other worker may 

 possibly be in a position to do so. As regards the second point, I am 

 not at all sure that it is actually necessary that the winter fat be more 

 deeply pigmented than that of the summer. The point is rather that 

 there should be more unosygenated fat peripherally at the time of the 

 autumn than of the spring change ; and that this is so I can myself 

 answer in the affirmative. It is full of significance, also, that the 

 muscle of the breeding Salmon becomes pale on transference of the 

 fat and pigment to the genitalia or for combustion as a source of 

 energy. 



III. The meaning of white in Domestic Animals and Vertebrates 



generally. 



If my conclusions be accepted, it seems that we may be hovering 

 somewhere near the explanation of the primary or physiological 

 meaning of many puzzles of animal colouration. The widespread 

 existence of white undersides in vertebrates — a fact only as yet 

 explained on purely secondary grounds (as by the ingenious suggestion 

 of Mr. Abott H. Thayer) — is now seen to have a direct connexion 

 with the main peripheral fat-tract of the body. The white rumps of 

 birds and mammals, the familiar "recognition marks" of Mr. Alfred 

 Eussel "Wallace, correspond to one of the next most important fat- 

 tracts, light neck- and ring-marks to yet another. 



I am inclined to push my theory even further, since I see in it the 

 explanation, often vainly sought for, of the marked extent to which 

 the white colour makes its appearance in domestic animals. Since 

 nearly all these animals derive their commercial value from their power 

 of accumulating fat, it is natural that, if my suppositions be true, the 

 pigmentation of the hair (or feathers) should be affected. I am aware 

 that in many breeds the appearance of the white patches is believed 

 to be quite irregular, and not to follow any definite order of fre- 

 quency as regards the regions affected. I feel sure, however, that 

 further investigations will show that this is not really the case. Thus 

 my own studies, unfortunately as yet incomplete, indicate that even 

 in such, at first sight, irregularly-marked animals as cattle, the 

 markings, although undoubtedly subject to very great latitude, tend 



