No. 611] FERTILITY IN SOUTHDOWN SHEEP 669 



Mean number of lambs per birth, 2.12 lambs. 



Standard deviation in number of lambs per birth, 0.76. 



Coefficient of variability in number of lambs per birth,- 

 35.78 per cent. 



Marshall (8) found after a study of the lambing sta- 

 tistics for various flocks of Scottish sheep for the years 

 1905, 1906, and 1907, that the percentage of lambs born 

 was, as a general rule, highest among sheep which had 

 been subjected to a process of artificial stimulation by 

 means of special diet at the approach of the breeding sea- 

 son. In some cases the number of lambs per ewes in the 

 ''flushed" flocks was nearly 200 per cent. Flocks which 

 were run upon special pasture upon the approach of the 

 tupping season generally produced a slightly larger per- 

 centage of lambs than those receiving no sort of special 

 feeding. Evvard (4) found among range ewes fed the 

 same ration that the fourteen heaviest gaining ewes at 

 time of breeding in his flock averaged 1.8 lambs ; the four- 

 teen medium gainers, 1.59; and the fourteen lightest 

 gainers, 1.44. 



EeLATION of MAMMiE TO FERTILITY 



Alexander Graham Bell (2) conducted an experimental 

 investigation on the relation of the number of mammae to 

 fertility. An unusually high fertility among a flock of 

 native sheep in Beinn Breagh, Nova Scotia, led Bell to 

 examine the ewes in order to discover some distinguishing 

 mark of the twin-bearing ewe. He found a certain num- 

 ber of ewes with one to two supernumerary nipples in an 

 embryonic, functionless condition. Of these abnormally 

 nippled ewes, 43 per cent, had twin lambs, while of the 

 normally nippled ewes but 24 per cent, produced twins. 

 This apparent correlation between multinipples and in- 

 creased fertility led to an extended series of experiments 

 to ascertain whether by selective l^reediiig, the super- 

 numerary nipples could be made functional, and whether 

 ewes with additional mammre in a functional condition 

 were more fertile than ewes with the normal number of 

 nipples. 



