Abstract
The experiments described here were designed to confirm and extend the work of YANDERS (1965) who observed a large and progressive decrease in the proportion of sons from older fathers. The term “sex ratio” here will mean the percentage of male offspring. Under my conditions a decreasing sex ratio from aging fathers (from 54% down to 46%) was observed, but it was limited to the first portion of eggs laid by equally aged mothers, and was absent, or reversed, as the successively brooded mothers continued to use up their stored sperm. In contrast to YANDERS’ results, all ages of fathers transferred, ouerall, approximately 50% each of X- and Y-bearing sperm as judged by the sex ratio among offspring of mothers who exhausted their sperm supply. The consequent difference in sex ratio between initial and later broods might mean a preferential utilization of Y-bearing sperm from younger males, and X-bearing sperm from older males.
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