GENETIC STUDIES OF RABBITS AND RATS. 



29 



parts of the body, or whether factors, independent one of another, 

 govern size in different parts of the body. The conclusion is reached 

 that the genetic agencies affecting size in rabbits are general in their 

 action, influencing in the same general direction all parts of the body. 

 The same would probably be found true for man and other mammals, 

 perhaps for vertebrates in general, but not for plants in which hor- 

 mone action is less in evidence. 



8. No linkage relation has been found to exist between size and 

 any simple (unifactorial) Mendelian character, such as albinism, 

 yellow coat-color, dilution, or angora coat. This result is in har- 

 mony with the view that unifactorial characters have their genes 

 located each in a single chromosome, while size is influenced by genes 

 located in many or all chromosomes. 



9. In rabbits, size differences correlated with sex are very slight. 

 In skeletal dimensions the adult male averages larger by 1 or 2 per 

 cent, but in weight females surpass males, particularly in the larger 

 breeds of rabbits; yet the differences are so small as not to disturb 

 appreciably the correlation coefficients based on data in which both 

 sexes are included. In ear-length no significant difference between 

 the sexes can be detected. 



TABLES. 



TABLE 1. Average weight in grams of rabbits of the several groups studied, at various ages. 

 Data used in the construction of figure 8. 



TABLE 2. Comparative weights in grams of the two sexes in the groups of rabbits studied. 



