2 Genetic Studies in Babbits 



made at an age of 18 weeks, and this, as will appear later, is too early 

 for trustworthy conclusions. Nor did he realize the marked sexual 

 differences which may occur, and which must, as we shall explain later, 

 be taken into account in work of this nature. He came to the con- 

 clusion that weight inheritance is blending in character, and that neither 

 dominance nor segregation in the Mendelian sense is recognisable. 



Castle's work was done before Nilsson-Ehle had put forward the well 

 known hypothesis of multiple factors. More recently MacDowell ('14), 

 in continuing Castle's experiments, has come to the conclusion that his 

 data are all in accordance with this hypothesis. MacDowell's work is 

 mainly concerned with skeletal measurements, and though periodical 

 weighings of his animals were made he does not attach much signifi- 

 cance to the results, pointing out various factors which tend to militate 

 against accuracy. 



Quite recently a few observations on the growth of rabbits have been 

 published by Da vies ('17) who states that when a small breed is crossed 

 with a medium sized one the young approximate to the size of the 

 smaller parent. But he admits that the cross was only made in one 

 way using the animal of the smaller breed as the mother. He is inclined 

 to consider that the reciprocal cross may give a different result, as he 

 holds that larger size depends more upon the mother than upon the 

 father. 



We cannot yet pretend to know very much about the inheritance of 

 weight in the rabbit. It is clear however that investigations of this 

 nature in the mammal do not yield such clean-cut results as in birds 

 (cf. Phillips ('12), Punnett and Bailey ('14)), 'and it is evident that a 

 great deal of laborious work must yet be done before we can understand 

 a process of which the theoretical, as well as the economic, importance is 

 so considerable. We do not therefore propose to discuss the matter 

 from a general point of view until we are in possession of fuller and 

 more complete data than those of which, we may now proceed to give 

 some account. 



General Account. Our experiments were started in 1912. The 

 breeds originally chosen were the Flemish \ one of the largest of rabbits, 

 and a strain of mixed Himalayan-Dutch-Havana origin which had been 

 formed in the course of some earlier experiments on coat colour. We 

 shall refer to this as the Flemish-mixed cross. The three breeds which 

 entered into this strain are all on the small side and on the whole differ 



1 We are indebted to the kindness of Dr B. N. Salaman for procuring these animals 

 for us. 



