372 SCIENCE PROGRESS 



In this report it is shown that in the season 1899 the por- 

 portion of ewes which failed to breed or which aborted their 

 lambs was 676 per cent., and that the number which produced 

 twins w^as about 30 per cent. The most fertile of all the breeds 

 was the Wensleydale, in which six flocks consisting of a total of 

 319 ewes produced a percentage of 177*43 lambs. The effects 

 of locality are also discussed, and there is an accumulation of 

 evidence which seems to indicate that the character of the district 

 is not without influence on the fertility of the breed. Thus the 

 records show that whereas the sheep belonging to the Lincoln 

 variety in Yorkshire produced an average of 47*57 per cent, of 

 twins, those in the home county had only 25*11 per cent., while 

 those in neighbouring counties produced 33*78 per cent. With 

 other breeds the variation in the fertility in different districts, 

 while quite noticeable, was not so pronounced as in the Lincoln 

 sheep. 



The report shows, further, that the fertility of a flock depends 

 greatly upon its management, that the quality and quantity of 

 the food supplied affect the condition of the sheep and so 

 influence their capacit}^ to breed, that some seasons are far more 

 favourable to fertility than others, and that sheep-stained pasture 

 {i.e. pasture on which sheep have recently been kept for some 

 little time previousl}") is often prejudicial to breeding stock. 



As a result of a recent investigation upon the reproductive 

 processes in sheep, it has been shown that (in the breeds 

 investigated) the normal percentage of Graafian follicles 

 discharging their ova at any single " heat " period does not 

 appreciably exceed the usual percentage of births at the lambing 

 season. It would seem, therefore, that a comparative scarcity of 

 twins at lambing time is almost certainly directly correlated with 

 an abnormally small number of ripe follicles in the ovary at 

 tupping time {i.e. during the breeding season). An unusually 

 low percentage of twins is closel}^ associated with barrenness. 

 This fact is generally recognised by flockmasters, and Mr. Heape's 

 statistics prove it very clearly. And since habitually {i.e. con- 

 stitutionally) barren ewes are a rarit}^ there can be little doubt 

 that barrenness is due normally to the same cause operating on 

 a more exaggerated scale — i.e. to the absence or great scarcity 

 of Graafian follicles available for ovulation during the tupping 

 season.^ 



' Marshall, Phil. Tra?is. B. vol. cxcvi. 1903. 



