FUTURE OF THE SCIENCE OF BREEDING 181 



out that they are not irreconcilable with the hypothesis of 

 multiple factors. 



For some years past I have been working at a case in rabbits 

 which is not dissimilar to that of Castle's rats. It is another 

 case where we are concerned with the extent of white in the 

 coat. The Dutch rabbit is characterised by a well-marked 

 pattern as regards the distribution of the white and pigmented 

 areas. Such rabbits not infrequently throw what the fancy 

 calls wasters animals in which there is a considerable 

 amount of irregular white patching on the pigmented area. 

 From animals of this type I have succeeded in establishing 

 a strain of rabbits which is almost completely white, and 

 breeds practically true. When crossed back with the Dutch 

 form the offspring are intermediate in appearance. Such 

 intermediates, mated together, produced not only inter- 

 mediates but also young of the two extreme forms some 

 like the Dutch and others almost white. My results as yet 

 are not sufficiently complete to attempt a formal scheme in 

 explanation, but those already attained seem more in harmony 

 with the hypothesis of multiple factors than with the view 

 put forward by Castle. 



Meanwhile the matter is of such fundamental importance 

 for the solution of breeding problems involving apparently 

 quantitative features like weight, size, yield and so forth, that 

 further experiments with different material ought to be under- 

 taken at the earliest opportunity. Only in this way can we 

 hope to disentangle the many issues wrapped up in the term 

 selection, and to place the operations of the practical breeder 

 upon a firm basis of ascertained and co-ordinated facts. 



I have mentioned but a few of the lines of inquiry which 

 at present are attracting the attention of the student of 

 genetics. There are others equally far-reaching and only less 

 developed because younger in point of time. 



There is, for instance, that concerned with the viability 

 or non-viability of particular forms of zygote. The yellow 

 mouse is a case in point. Yellow is dominant to other colours 

 such as agouti, black or chocolate. But all yellow mice are 

 heterozygous for the yellow factor. Yellows bred together 



