1903.] 



Observations on the Sex of Mice. 



37 



Number. 



Doe. 



Number in 

 litter. 



Surviving 

 males. 



Surviving 

 females. 



Eaten. 





B 2,1 



6 



4 



2 





56 



B 22 



7 



5 



2 







B 3 * 1 



5 



4 



1 







B 3 - 2 



10 



6 



4 





59 



c 1,2 



7 . 



1 



5 



1 







8 



2 



6 







Q1.3 



8 



5 



3 







55 



8 



6 



2 







55 

 pi.l 



7 



6 



1 







5 



2 



1 







D 2,3 



5 



5 









J)3-3 



4 



2 



2 







CJl.2-1 



5 



2 



3 





68 , 



C 1.2.2 



7 



2 



5 





69 



C 1.2.2.1 



10 



2 



6 



2 



70 



55 



7 > 



3 



4 





71 



Gr 



3 



\ 



2 





72 



55 



7 



5 



2 





73 



H 



8 



6 



2 









487* 



231 



211 



45 



This table shows that 487 young were produced in 73 litters, thus 

 giving an average of 6 • 7 for a litter. There are 45 litters of 7 or over, 

 and 28 of under 7. These we may speak of as large and small litters 

 respectively. If the number of young in the 45 large litters is added 

 up it amounts to 356, and of these 164 (46 per cent.) were males ; 

 155 (43 '5 per cent.) females; while 37 (10*5 per cent.) were eaten and 

 their sex undetermined. Similarly if the number of young in the 

 28 small litters is taken we get a total of 131 ; of these 67 (51 percent.) 

 were males; 56 (43 '7 per cent.) females; while 8 (6 per cent.) were 

 eaten. Tabulated these results are as follows : — 



cf $ Eaten 



per cent. per cent. per cent. 



Large litters (over 6) 46 43'5 10-5 



Small litters (6 or under) ... 51 43 6 



This result suggests two conclusions — firstly, that in a large litter a 

 greater percentage of young is eaten by the mother, which is, perhaps, what 

 one would expect, and, secondly, that in small litters there is a slightly 

 greater percentage of males than in large ones. Other things being 

 equal, one might fairly suppose that, in a small litter, each individual 

 embryo would be better nourished than in a large litter, and this 



* The records of the six does with which the buck S was placed in a large cage 

 ha\e not been added in, because we have no means of knowing bow many were 

 eaten. 



