28 



SIZE INHERITANCE IN RABBITS. 



made when convenient, and in December there were several litters a? 

 large as those born in the summer. These experiments did not indicate 

 that the mother's age had any influence. 



The question of sex differences was investigated in the following 

 manner : Litters with an equal number of males and females (or equal 

 within one) were selected ; the total number of males was 35, the total 

 number of females 37; the averages of the measurements of the males 

 were now compared with the averages of the same measurements for 

 the females. The measurements of the males exceed those of the 

 females in six cases ; the reverse is true in ten cases. But the differences 

 are not large and are probably without significance except in the four 

 measurements in which alone they amounted to as much as a millimeter. 

 These four measurements are P. O., P. M., F., and T. 



TABLE 2. Comparison of males and females as regards average bone measurements. 



Apparently there is a difference between the two sexes in the position 

 of the anterior margin of the palate, which lies farther forward in the 

 females than in males. The difference amounts to about 1.5 mm. 

 Consequently, in males the measurement P. 0. is less than in females, 

 and the measurement P. M. is greater, by about 1.5 mm.; the total 

 skull length is substantially the same in both sexes. 



The other apparently significant difference is in the long bones of 

 the hind leg. In males the femur and tibia are 3 or 4 mm. longer than 

 in females of the same size in other respects. This means that male 

 rabbits have slightly longer hind legs than females. 



The sexual differences in these four measurements amount to between 

 3 and 4 per cent, not enough to disturb materially the statistical results 

 based on these measurements. In none of the remaining measurements 

 can a sexual difference be detected. 



