ANIMAL BREEDING. II9 



relative!}^ simple one for the study of an aspect of heredity 

 which may have an important economic application. 



Of the experiments with rabbits, the most important have 

 been those dealing with fur pattern, and this investigation is 

 still going on. While the work has an obvious practical applica- 

 tion in connection with fur production, this is not regarded as 

 its most important bearing. The main object of the research 

 is to ascertain the principles underlying the inheritance of 

 pattern — a question which is of widespread importance in 

 relation to most of our domesticated animals. It is well-known 

 that in most classes of animals forms occur with white markings. 

 The extent of these markings varies greatly, and a graded 

 series can generally be found with a self-coloured animal at one 

 end of the scale, and an almost white at the other. This is the 

 case in rabbits. A cross between the two extremes produces 

 animals with some white, and when these are bred together in 

 sufficient numbers the whole series of forms — ranging from 

 almost white up to self-colour — is obtained. At the time the 

 experiments were undertaken it was generally regarded as 

 doubtful if the general laws of inheritance applied to such a 

 case. It was thought that the amount of white depended upon 

 a process of selection, and could be increased or decreased at 

 will. As these graded series are commonly found in animals, 

 and moreover apply to many other qualities than pattern, it 

 was important to ascertain whether the generally accepted view 

 of inheritance was justified, or whether the inheritance of pattern 

 is really due to the combination of a few simple inheritable 

 factors. The work at Cambridge during the past twelve years 

 has shown that the second explanation is probably the correct one. 



A further series of experiments, dealing with weight in rabbits, 

 has been in progress for the past ten years. These experiments 

 were designed with the idea of making an investigation of 

 mammals on lines parallel to the experiments with poultry 

 alread}^ alluded to. A similar procedure was adopted, viz., 

 a cross between a very small breed, the Polish, and one of the 

 largest breeds, the Flemish Giant. As in the poultry, the first 

 crosses proved to be intermediate in size, but when bred together 

 they have so far failed to produce anything approximating to 

 the Flemish, though they have given animals almost as small 

 as the Polish. Why the large size was not produced is a problem 

 at present under investigation. Through the systematic weighing 

 of all animals in this series of experiments, interesting data are 

 being accumulated in connection with fecundity and early 

 maturity, and it is hoped that they will eventually throw light 

 upon inbreeding and crossbreeding — perhaps the most important 

 of all problems connected with stock raising to-day. 



