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HELEN DEAN KING 



of the inbred series where the average size of the first four litters 

 was as low as that in the stock series (tables 1 and 2). In the 

 inbred series as a whole, the average size of the litters was 0.8 

 greater than that in the stock series. Even if the previous finding 

 of 7.0 be taken as the norm for litter size in the rat, the difference 

 between the average size of the litters in the inbred strain and the 

 norm chosen is 0.5. This difference is great enough to preclude 

 the possibility that it was due to chance, and it cannot be attrib- 

 uted to the differential action of environment, since stock and 

 inbred rats were constantly under the same environmental con- 

 ditions. According to these findings, fertility in the inbred 

 strain of Albinos, in as far as it may be judged by the size of the 

 first four litters cast by a large number of females, was greater 

 than the fertility in stock Albinos that were not inbred. 



B. Frequencies of litter size 



According to the several series of observations that have been 

 recorded, there is a wide range in the size of the litters cast by 

 Albino females. Kolazy ('71) reports litters containing from five 

 to seventeen young, although Crampe ('84) states that he never 

 found even fourteen young in a litter of albino rats. Litter size 

 varied from four to twelve in the series of Albinos studied by 

 Kirkham and Burr (15) ; while in the litters recorded by King and 

 Stotsenburg ('15) the range in size was from two to fourteen. 



Data for litter frequencies in the two series of inbred rats are 

 shown in table 8. 



TABLE 8 



Showing the frequencies of litter size in the two series of inbred rats 



