SUCKLING — EMBRYONIC DEVELOPMENT IN MICE 



53 



TABLE 2 



Data of all mice used in an experiment to determine the effect on developing embryos 

 of the suckling of a fixed number of young. In this experiment all litters ivithin 

 twelve hours of their birth were reduced to four young. Stage of embryonic de- 

 velopment in terms of actual age of similar embryos from non-suckling females 



litter or with any other factor is to be sought in the first part of 

 this paper, where the irregular influence of the tennination of 

 suckling by a full litter is conclusively shown. Add to this the 

 fact that under normal circumstances the suckling young begin 

 to eat sohd food at about the time implantation occurs in females 

 which are simultaneously pregnant, and the evidence here 

 presented all indicates that after full suckling ceases, whether by 

 removal of the litter or weaning matters not, the inhibition to 

 implantation is withdrawn or overcome at a widely different rate 

 in different females. Therefore, even when the number suckled 

 is the same, the sets of embryos show no constant rate of develop- 



