vi] Pink Eyes in Coloured Types 



in 



Deficiency of Eye-Pigment in some Coloured Types. 



In the eyes of actual albinos, destitute of pigment, the 

 eye has the well-known pink appearance. This is due to 

 the admission of light through the partially transparent 

 iris. Generally speaking such great deficiency of ocular 

 pigments occurs only in total albinos, but to this rule there 

 are a few remarkable and interesting exceptions. 



The best known example is the so-called Himalayan 

 Rabbit*. In it the eyes look like those of the pure albino 

 though having a trace of pigment. At birth Himalayans 

 are white or nearly so, but soon the muzzle, ears, tail, and 

 feet assume a deep chocolate-black. This type behaves as 

 a recessive to the normal grey, and to black, and it is a 

 normal dominant to the pure albino. Hurst however found 

 that Himalayans, though obviously pigmented, may carry 

 the factors for black and for self-colour, without any in- 

 dication of such factors being manifested in their own 

 colour or in its distribution. Recent experiments made 

 by Punnett have given the same result. 



The next example of the pink eye present in an animal 

 not devoid of colour is seen in certain " Japanese Waltzing" 

 mice. 



The "waltzing" is a peculiar vertiginous spinning to 

 which those animals are subject. I understand that the 

 exact physiological nature of this movement has never been 

 fully elucidated, but the condition has been shown to be 

 often, if not always, associated with malformation of the 

 auditory labyrinth. As already mentioned, the waltzing 

 character behaves as a Mendelian recessive to the normal 

 habit. 



Such waltzing mice exist in various colours, some having 

 ordinary black eyes, others pink eyes. Various colours also 

 may occur in the coats and we have not yet complete 



* Darwin gives (Animals and Plants, ed. 2, 1885, I. p. 113) facts as to 

 the production of Himalayans by crossing Silver-greys. In the light of 

 present knowledge it is no longer possible to accept these experiments as 

 evidence of an original production of the variety. Presumably the case 

 was only one of the reappearance of a recessive form, and indeed Darwin 

 adds the remark that he had " recently been assured the pure Silver-greys 

 of any such breed occasionally produce Himalayans." 



