HELEN DEAN KING 



as yet, appeared. Cuenot ('99) examined thirty litters of albino 

 rats, containing 255 young, and found a sex ratio of 105.6 cf: 

 100 9 ; data for 1089 litters of stock Albinos, collected by King and 

 Stotsenburg ('15), gave a sex ratio of 107. 5cf: 100 9- Neither 

 of these determinations seemed to furnish a proper standard for 

 comparison with the sex ratios obtained in the inbred strain, 

 even though they differed by less than two points. The number 

 of individuals examined by Cuenot was too small to give results 

 of much statistical value. The sex ratio given by King and 

 Stotsenburg was based on the findings for a relatively large 

 number of animals, but the litters recorded were, for the most 

 part, cast by females that had not reached the height of their 

 reproductive activity. The sex ratio among the offspring of 

 young females could not justly be taken as a norm for the Albino 

 strain in general, since it has been shown that in the albino rat 

 the sex of the young seemingly depends, to a certain extent, on 

 the age of the mother (King, '16 a). 



In order to ascertain the normal proportion of the sexes in 

 the strain of Albinos from which the inbred animals were taken, 

 I obtained the complete breeding history of a considerable num- 

 ber of stock females during the past four years. As all of these 

 individuals were reared under the same environmental conditions 

 as the inbred rats, the sex ratio among their young would seem 

 to be a suitable standard by w^hich to judge the sex ratios found 

 in various generations of the inbred animals. To make the ratios 

 more strictly comparable, the data for only the first four litters 

 of the stock series were used in computing the sex ratio which 

 was to serve as the norm. These data, arranged by litter groups, 

 are shown in table 1. 



TABLE 1 

 Showing the sex ratios in the first four litters of a series of stock albino rats 



