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Eesearch in Animal Breeding. [June, 



in the rabbit, ranging between the self-coloured animal with 

 a touch of white on the nose or on a paw, and an animal 

 completely white except for a touch of pigment round the 

 eye and at the root of the tail (Plate 2, Fig. 3). Such a 

 continuous series can in fact be bred in the F2 generation from 

 a cross between a self-coloured animal and one of these almost 

 white ones. The problem here again was to determine whether 

 such an apparently continuous series could be expressed in 

 terms of a few definite factors, or whether some other explana- 

 tion had to be sought. 



The case was of more than usual interest because Professor 

 Castle, working at a similar case in rats, had put forward the 

 view that the factor itself could be changed by " selection." 

 Were this view upheld by experimental research, it is evident 

 that we should have to give up the conception of the relative 

 permanence * of the factor which forms the basis of the 

 factorial 'theory, and with it that hope of control over breeding 

 operations which the definite and permanent factor signifies. 

 The results of our experiments with rabbits did not bear out 

 Professor Castle's view. We found that a comparatively simple 

 interpretation on factorial lines would cover the facts.* More- 

 over, Professor Castle himself has recently given up his earlier 

 view, and considers that an orthodox explanation, in terms 

 of the factorial theory, is adequate. We have mentioned the 

 case here because the idea that the factor can be influenced 

 by selection " is to be found in text-books that are widely 

 read. It may serve to prevent misunderstanding if it is reahsed 

 that the view is no longer supported by its originator. 



As we have already stated, a cross between a self-coloured 

 animal and a " White Dutch " gives Fl animals with a 

 small but varjdng amount of white, and in F2 a full range 

 from Self to White Dutch. In such a series, however, the 

 gradual increase of the White occurs in a more or less orderly 

 fashion. It begins with the tip of the nose or muzzle, the tips 

 of the fore paws, and the " blaze " ; it then invades the neck, 

 shoulders and fore limbs; at a more advanced stage we reach 

 the typical pattern of the Dutch rabbit (Plate 2, Fig. 1) ; later 

 on the pigmented area round the eyes is reduced and the 

 coloured area of the body becomes patched with white, giving 

 rise to the ''spotted Dutch" (Plate 2, Fig. 2); further 

 reduction of the pigment eventually results in the White Dutch 

 (Plate 2, Fig. 3). 



* "The Genetics of the Dutch Rahbit— a Criticism," by R. C. Piinnett: 

 Journal of Genetics, Vol. IX, 1920. 



