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VII. 



ABSTEAGT OF A PHYSIOLOGICAL HYPOTHESIS TO EX- 

 PLAIN THE WmTER WHITENING OF ITAII^^IALS AND 

 BIRDS INHABITING SNOWY COUNTRIES, AND THE 

 MORE STRIKING POINTS IN THE DISTRIBUTION OF 

 WHITE IN VERTEBRATES GENERALLY. 



By captain G. E. H. BARRETT-HAMILTON, B.A., 

 F.Z.S., M.R.I.A. 



Eead May 11, 1903. 



Although so much attention tas been attracted to the subject of 

 the winter whitening of mammalg and birds, no theory has, so far as 

 I know, been advanced to explain the physiological meaning of this 

 phenomenon. On the other hand, Naturalists seem to be perfectly 

 agreed as to the advantages in a protective sense which the animals of 

 snowy countries derive from their seasonal change, it being regarded 

 as one of the most perfect of known instances of adaptation to 

 environment. I ventui-e to believe that scientific investigations have 

 now brought together facts sufficient to shed a glimmering of light 

 upon the physiological or primary meaning of the white seasonal 

 colour changes. I therefore put forward the following hypothesis, 

 which is based upon an intimate connexion between fat and animal 

 pigmentation. 



I. The connexion letween Fat and Vertebrate Pigmentation. 



While I was va. South Africa I was greatly siu-prised at the 

 number of species of birds in which the fat is more or less deeply 

 coloured, rich yellow, orange, or even reddish. I further fomid a 

 correspondence, often quite remarkable, between the coloiu' of such 

 fat and the pigmentation of the feathers. Thus in bii'ds in which 

 yellow appears in the plumage the fat is usually of a correspondingly 

 yellow or orange tint. Instances of this may be found in the Great- 

 tailed Widow Bii'd, the Cape Long-Claw, the Masked Weaver Bird, 

 and the Red and Taha Bishop Birds. 



In other birds, although more rarely — to include some other than 

 South African species — as the Chough, Stork, and Flamingo, the 



R.I. A. PROC, VOL. XXIV., SEC. B.] 2 C 



