50 



The Journal of Heredity 



December, 1899, at a time when the 

 ewes were bej^inning to lose weight on 

 account of failing pasture — after which 

 they remained in reduced condition 

 until their lambs were bom. Under 

 these circumstances 88.5% of the lambs 

 were males; whereas in the Bcinn 

 Bhreagh flock, where the ewes had 

 been specially fed, 72.2% were females 

 (of the Alarch-boni lambs). 



"These facts s^eem to indicate that 

 perhaps, after all, the special feeding in 

 the autumn of 1899, may have been 

 responsible for the large proportion of 

 females bom in 1900. 



DIFFERENCES IN WEIGHT. 



" If the nutrition of the mother during 

 the earh' period of gestation is an ele- 

 ment in determining the sex of her off- 

 spring, we may reasonably hope to 

 observe some characteristic differences 

 of weight between the mothers of males 

 and the mothers of females at this 

 period. The records of the Beinn 

 Bhreagh flock are suflficiently volumi- 

 nous to enable us to examine this point. 



"x'\n inspection of the figures shows 

 that the differences of weight are slight, 

 but, on account of the considerable 

 numbers involved it may well be that 

 they are significant. At the beginning 

 of October, before mating had been 

 accomplished, the average weights of 

 the two classes of ewes (male-bearing 

 and female-bearing) were the same. 



"The average male-bearing ewe in- 

 creased in weight np to the end of 

 October, after which there was a 

 decline: The average female-bearing 

 ewe, on the other hand, continued to 

 gain in weight all through November so 

 that by the end of that month the 

 average female-bearing ewe outweighed 

 the male-bearing — a superiority re- 

 tained during the subsequent decline. 



"Such being the results in the case 

 of matings during the decade 1890- 

 1899, we added the data for the lambs 

 bom in March 1900, from matings 

 which occurred in October, 1899. In all 

 these cases the mothers were specially 

 fed, as described above, up In the time 

 of mating. 



"Here again we observe a reversal in 

 the relative weights of the two classes 



of ewes. The male-bearing ewes, on the 

 average, outweighed the others at the 

 beginning of the period of gestation, but 

 after mating lost weight so much more 

 ra])idly than the female-bearing ewes 

 that the latter soon became the heavier. 



MOTHERS OF TWINS HEAVIER. 



"In order to afford data for more 

 detailed examination of changes of 

 weight, these ewes were weighed once a 

 week during the whole period of gesta- 

 tion. We found that the mothers of 

 twins were above the average of the 

 flock in weight; and the mothers of 

 single lambs were below the average. 



"Among the single-bearing ewes the 

 mothers of males averaged less in weight 

 than the mothers of females. It was 

 noticed that the mothers of males were 

 losing in weight at the time of mating, 

 and immediately after mating, whereas 

 the mothers of females substantially 

 retained their weight for some time 

 after mating. 



"Among the twin-bearing ewes there 

 were none who had male lambs ex- 

 clusivel^^ Those who had male as well 

 as female lambs were losing in weight 

 at the time of mating and immediately 

 after; whereas those who had female 

 lambs alone were increasing in weight at 

 the time of mating, and, though the 

 weight dropped afterwards, did not 

 continue to drop but remained sub- 

 stantially on a level for several weeks. 

 Those who had twins, male as well as 

 female, were nearly 12 pounds heavier 

 than those who had twin females alone, 

 at the beginning of the period of gesta- 

 tion; but subsequently lost weight so 

 rapidly that seven weeks after mating 

 they had lost their superiority in this 

 regard. 



"All these ewes were given a special 

 feed of oats twice a da\' up to the time 

 of mating, after which the extra feed 

 was discontinued, the ewes then deriving 

 their sole nourishment from the i)asturc. 



"The aggregate and average weekly 

 weights, in the autumn and winter of 

 1899, of the 20 ewes who had single 

 lambs in March, 1900, and of the eight 

 ewes who hail twin lambs, were also 

 compiled, witli similar results. Not 

 only were the twin-bearing ewes very 



