24 



BIOLOGY 



the average individual birth weight for the male as 4.72 grams 

 and for the female 4.56 grams. 



The data from these 11 stock litters used for tables 3, 4, 5, 6 

 have not been published elsewhere in a separate form. In the 

 paper by King ('15) , however these data are combined with corre- 

 sponding data for the inbred Albinos to form similar tables. 

 The results obtained from the stock data here given are quite in 

 agreement with those from the combined data of King ('15) . The 

 birth weight may be modified by a series of conditions as shown 

 in the following tables. 



TABLE 3. 

 Influence of the age of the mother on birth weight 



Table 3 shows that with increasing age up to 217 days the indi- 

 vidual birth weight increases with the age of the mother. At 

 the same time it is to be seen that the body weight of the mother 

 also increases. 



When the same data are arranged according to the bodyweight 

 of the mother, we get the relations shown in table 4. 



TABLE 4 



Influence of weight of mother on birth weight 



Here the birth weight increases with the increasing body- 

 weight, but the age is also increasing in the successive groups. 

 The influence of the size of the litter on birth weight does not 



