REPRODUCTION 



157 



When the young are removed from the mother at birth the 

 ovaries fail to show the loss in weight which occurs during the 

 later days in normal lactation. 



In another series of 52 cases, Evans and Bishop ('23) deter- 

 mined that 69 per cent of the discharged ova were implanted 

 and that of these latter about 9 per cent were resorbed. Out 

 of three series, 4.2 per cent were born dead. 



1.1 9.5 103 8.0 



9.t 8.5 '100 U 9.0 8.0 8.0 15 



1.0 



Chart 18 Giving in milligrams the weight of both ovaries at fifteen intervals 

 during lactation. The mean value for the period is indicated by a heavy circle. 

 The individual values by a cross. Days entered below and the average number 

 of young above. The mean ovulating weight of the ovaries is 49 mgm. 



In the Institute colony about 2 per cent of the young are dead 

 at birth a proportion similar to that found in man but the 

 ratio of the dead born males is 129 to 100 females, King ('21). 



The number of litters born is only slightly less (97.5 per cent) 

 than that to be expected from the "placental sign." Of the lit- 

 ters born, about 86 per cent were successfully suckled, and at 

 weaning the mothers were 6.4 per cent heavier than at littering, 

 Evans and Bishop ('23). 



