130 



B. SUMNER, M. E. MCDANIEL AND R. R. HUESTIS. 



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FIG. i. Above: the sex ratio of Peromyscus for each month of the year, 

 computed from all the material. The continuous line is based upon the date 

 of birth, the broken line upon the date of conception. Ordinates indicate sex 

 ratios (number of males per hundred females). The figures along the graphs 

 denote the number of individuals born (or conceived) during each month of 

 the year. 



Below : mean size of brood for each month of the year. Figures along 

 line = number of broods. 



