No. 595] 



SEX CONTROL IN PIGEONS 



401 



ductive of " strength." The larger eggs both of clutch 

 and season more often display "weakness." And in 

 passing we might note that by the procedures involved 

 in these sex-series it is possible to graduate the fatal 

 dosage, and in great measure to predict which of particu- 

 lar germs must come to an end first. 



The fourth kind of fact pertaining to the eggs of this 

 series, proceeds from the results of more than 800 chem- 

 ical analyses of individual eggs. The results of earlier 

 studies of this nature were described in 1911 s and 1912 

 more fully than time limits will here permit ; but the na- 

 ture of these results can be noted with the help of Chart 

 3. It will be observed that not only does the size of the 

 egg increase with its later position in the series, i. e., 

 with lateness of season, but the percentage of energy- 

 yielding or stored materials increases as much as, or pos- 

 sibly more than, is indicated by the size— or net weight — 

 of the yolk. 



The importance, for our present purpose, of the re- 

 sults of these analyses is that they conclusively show (1) 

 that the male-producing egg of the spring is an egg that 

 stores less material than does the female-producing egg 

 of the autumn. (2) That the male-producing egg of the 

 clutch stores less material than does its female-producing 

 mate. (3) That the eggs of old females store more ma- 

 terials, and— as has been noted-yield a higher percen- 

 tage of females, than do birds not old. Therefore, it be- 

 comes evident that the egg of female-producing tendency 

 is one whose storage metabolism is high, as compared 

 with eggs of male-producing tendency. The analyses 

 show that during the season successive clutches present 

 higher and higher storage, i. e., the earlier clutches store 

 less— are more male-like; the later ones all store more- 

 are more female-like ; and as we have seen, the eggs of 

 the low storage period give rise to males, those of the 

 high storage period produce females. Here we obtain a 

 close view of that upon which sex difference rests. Un- 



see Science, X. S., Vol. 4<V> -n'.::. Man-h 22. 1912. 



