No. 595] 



SEX CONTROL IN PIGEONS 



407 



and as affected by the procedure of overwork, may be 

 more quickly said with the aid of the charts. 



One chart (only Chart 2 is reproduced here) shows the 

 weight average of each individual hatched during the 

 year, from two simultaneous matings of alba X risoria. 

 Series I is from an older pair, previously overworked; 

 series II is from a younger pair, little— or not at all— 

 previously overworked. It will be noted that series I is 

 throwing large eggs, a predominance of females, and that 

 the size of the offspring— even of the. males— is prevail- 

 ingly that of the females rather than the males of the 

 parent species. 11 Series II is throwing smaller eggs, a 

 nearly equal proportion of the sexes, ,except at the end 

 of the season, and the size of the offspring is decidedly 

 larger than in series I ; and, in fact, approximates to the 

 size of the males of the parent species. In both of these 

 series it will be observed that size of offspring 12 is also 

 correlated with the order of eggs in the clutch. 



For series I, we have complete data for the year pre- 

 ceding and the year following the term covered by the 

 chart. The weights for the former were: A v. for gTs 

 172 gr. ; $'s 166 grams. For the succeeding year— early 

 1915— these weights are J's 157 gr. ; ?'s 156 gr. Clearly, 

 during the three-year period a change in size of offspring 

 is progressively occurring; and the change runs from a 

 size comparable to that of the males of the parent species, 

 to a final size that is somewhat below that of the females 

 of the parent species. The egg-size was known in this 

 same series to have progressively and simultaneously 

 changed from greater male-producing tendency to a de- 

 cided female-producing tendency. 



The seventh line of study intended to analyze the sea- 

 sonal and clutch deliveries of the sex-controlled series is 

 concerned with arrangements by which the sex-behavior 

 of the birds from such series is tested. In these pro- 



« The males, in both of these species, average 10-15 grams heavier than 

 the females; the risoria birds are slightly larger on the average (5-10 

 grams) than alba. 



i 2 The weights given for individual birds represent the average of the 

 monthly, or bi-monthly weights- for the year. 



