34 



INHERITANCE IN RABBITS 



Cross 8. — Quarter-blood Lop x Three-quarter-blood Lop. 



A single mating of this sort produced a litter of 3 young, all very sim- 

 ilar and close to the mid-parental ear-length. (See table 25.) The 

 observations were discontinued when the young were 14 or 16 weeks old, 

 but the mid-parental ear-length of the parents, when they were 20 weeks 

 old, had already been closely approximated. The deviations were —2, 

 — 5, and —5 mm. If growth progressed normally from the age of 14 or 

 16 weeks on, they would surely have attained the adult mid-parental 

 ear-length, viz, 167.5 mm. 



LIMITATIONS OF THE DATA STUDIED. 



In attempting to draw conclusions from the statistics presented in the 

 foregoing pages, one must bear in mind certain of their Hmitations and 

 imperfections. 



(i) Ear-length is modified to some extent by external conditions. If the 

 young rabbit is well nourished up to the age of 20 weeks, its ear-length 

 will be greater than if it is poorly nourished, other conditions being equal. 

 While we have attempted to give our rabbits the best of care at all sea- 

 sons, it is inevitable that the quality of food supplied at different seasons 

 of the year should vary, and with variation in the quaUty of the food goes 

 variation in the growth rate. This renders it difficult to compare with 

 each other, as regards ear-character, rabbits reared at different seasons 

 of the year. But it has been impossible for us to rear enough rabbits at 

 any one season to afford adequate material for comparisons. Hence we 

 are forced to utihze material produced at different seasons of the year. 



(2) Size of litter is of some consequence in determining the growth rate 

 of a rabbit. If there are several young in a litter each gets a smaller 

 amount of food during the period of lactation than it would have received 

 had the litter been smaller. Our material, however, is not extensive enough 

 to allow us to institute comparisons merely between litters of substantially 

 the same size. 



