RELATION TO GENERAL BIOLOGICAL PROBLEMS 119 



is established as an inherited specific character is the 

 only conclusion that the facts admit. 



The question of whether twinning in ruminants is 

 hereditary is dealt with by various wi;iters. The ex- 

 periments of Alexander Graham Bell furnish the best 

 available evidence on this point. In 1889 he purchased 

 a farm at Beinn Bhreagh in Nova Scotia and found 

 himself in possession of a flock of sheep. In the spring 

 of 1890 one-half of the lambs born on the place turned 

 out to be twins. Evidently he had a race of sheep 

 with an unusually strong twinning tendency, and it 

 became an object of interest to discover just which 

 ewes were twin-bearing and whether they showed any 

 easily recognizable correlated characters. Bell says: 



Upon examining the milk-bags of the sheep, a peculiarity was 

 observed which was thought might be significant. Normally, 

 sheep have only two nipples upon the mUk-bag, but in the case 

 of several of the sheep examined, supernumerary nipples were 

 discovered which were embryonic in character and not in a 

 functional condition. Some had three nipples in all, and some 

 four. Of the normally nippled ewes 24 per cent had twin lambs; 

 but of the abnormally nippled 43 per cent had twins. The total 

 number of ewes, however, was so small (only 51) as to deprive the 

 percentage of much significance. Still the figures suggested a 

 possible correlation between fertility and the presence of super- 

 numerary nipples, and it seemed worth while to make an extended 

 series of experiments to ascertain (i) whether, by selective breeding, 

 the extra nipples could be developed so as to become functional, 

 and (2) whether the ewes possessing four functional nipples instead 

 of two would turn out to be more fertile than other sheep and 

 have a larger proportion of twins. 



Apparently no difficulty was experienced in develop- 

 ing the embryonic supernumerary nipples into func- 

 tional organs, and by 1904 nearly all of the ewes on the 



