EAR-SIZE 35 



(3) It is the belief of fanciers that a warm, moist atmosjihere, during 

 the period of active growth of the ears, favors the attainment of large 

 ear-size. This view we have not been able to juit to an experimental 

 test, but we are inclined to think that the temperature and humidity arc 

 much less important factors than abundant food supply. 



(4) Rabbits of the small, short-cared races have a shorter growth period 

 than the larger races. Their ears are more likely to be full-grown at 20 

 weeks of age than are those of loj)-eared rabbits. Therefore, in comi)aring 

 rabbits of ditTerent ancestry at the same age, say 20 weeks, one is in dan- 

 ger of underestimating the ear-length of the larger-sized rabbit. 



(5) A cross between rabbits of entirely different races is likely to result 

 in young of unusual vigor, which causes them to attain a greater weight 

 and ear-length than the hereditary constitution of either race by itself 

 would result in. This is illustrated notably in cross 3, page 20. Supe- 

 rior size or ear-length, induced by crossing, we should not e.xpcct to be per- 

 manent in later generations. 



(6) Disease frequently interrupts the orderly progress of a growth-curve 

 and necessitates the omission altogether of certain series of observations. 



CONCLUSIONS. 



Notwithstanding these limitations, which manifestly restrict the scope 

 of our conclusions, certain generaUzations are clearly justified. 



(i) A cross between rabbits differing in ear-length produces offspring 

 with ears of intermediate length, varying about the mean of the parental 

 ear-lengths. 



(2) It is immaterial whether the larger parent was father or mother; 

 the result is the same in either case. As regards ear-length, then, we may 

 say, reciprocal crosses give the same result. This shows that ear-size is 

 a character inherited with equal intensity through father or mother. 



(3) A study of the offspring of the primary cross-breds shows the blend 

 of the parental characters to be permanent. No reappearance of the grand- 

 parental ear-lengths occurs in generation F2, nor are the individuals of 

 that second generation as a rule more variable than those of the first gener- 

 ation of cross-breds. Fig. 3 shows the most extreme case of "scatter" in 

 F2 that we have observed. Yet the variation in this case is no greater 

 than among the young of lop-eared rabbits bred inler se. 



(4) The extreme range of variation in ear-length among short-eared 

 rabbits is about 10 mm.; in lop-eared rabbits it is two or three times as 

 great, or from 20 to 30 mm. Among rabbits produced as crosses of vari- 

 ous sorts between short-eared and lop-eared rabbits the range of varia- 

 tion in ear-length is mostly intermediate in amount. 



(5) The form of the growth-curve for ear-length from the age of 2 weeks 

 on is convex upward, indicating a steady diminution in the daily growth 

 increment. 



