SEX-RATIO OF THE DEER-MOUSE. 139 



ences among the sex ratios, and that some of these differences 

 would seem to be of statistical significance. 



For man, Heape (1909, 19090-) has compiled data, based upon 

 census records of the births of more than 175,000 whites and 

 negroes in Cuba. Unfortunately he does not give the number of 

 births nor the sex ratios, for every month of the three-year period 

 with which he deals, but only the figures for certain selected 

 months of each year, namely, those showing the highest and lowest 

 birth rates. We are therefore obliged to take Heape's conclu- 

 sions to a large extent upon his own authority. 



There are, he tells us (19090) two seasons of high birth rate, 

 a major one in July and August, and a less marked one in Novem- 

 ber and December. There are likewise two seasons of low birth 

 rate, the chief of these being in January and February, the lesser 

 one in September. During the periods of high birth rate, we 

 are told, the sex ratios are relatively low (102.9 to 105.5 for 

 whites; 93.3 to 104.1 for negroes). During the periods of low 

 birth rate, on the other hand, the sex ratios are relatively high 

 (106.2 to 113.0 for whites; 99.8 to 116.3 for negroes). Thus, 

 there are "two sharply-defined breeding seasons each year . . . 

 experienced by both whites and colored at the same time," one of 

 these being more marked than the other. 



These breeding seasons, Heape contends, are not related to the 

 periods of the year at which marriages are most frequent. He 

 seeks for correlations between certain meteorological conditions 

 and the periods at which conceptions occur with greatest and with 

 least frequency. The former periods would naturally fall in 

 October-November and February March, the latter in April- 

 May and in December. In regard to these seasonal correlations, 

 Heape states : " Reference to records of temperature, barometric 

 pressure, humidity, etc., shows that these bursts of reproductive 

 activity always take place at times when there is a marked change 

 of climate; the one in the autumn . . ., the other in the early 

 months of the year ... it is obviously not a definite temperature, 

 but the experience of a change of temperature which induces this 

 boisterous generative activity' (1909, pp. 35, 36). Likewise, 

 " my tables demonstrate that the greatest excess of females is 

 produced at times of greatest fertility." 



