338 riddle: control of sex ratio 



masculinity, for as we shall see later a part of these females are 

 strongly masculine, and indeed they show various grades of 

 masculinity. The evidence against a differential maturation as 

 a basis for an interpretation of the controlled sex ratios of 

 pigeons is so strong as to cause its rejection, even if the essential 

 constructive facts on the nature and basis of sex had not yet 

 been learned. 



The storage metabolism of many male- and female-produc- 

 ing ova, both in reference to egg of clutch and to position in 

 the season, has been determined by means of the bomb calori- 

 meter. The method is very accurate and the results are entirely 

 convincing. The stored energy, or heat of combustion, of 

 nearly 400 egg-yolks has been determined. One such series of 

 determinations, (made in 1914) in which all available eggs of 

 a particular female were burned is shown on Table 8. It will 

 there be seen that the first clutch or pair of the season bore a 

 higher caloric value than the second pair, but is otherwise the 

 smallest of the year. Beginning with the second clutch laid 

 in June the succeeding clutches to December 1 bear higher and 

 higher heat values. In all clutches too, except the very first, 9 

 the second eggs show a higher storage of heat units than do the 

 first of the clutch. Here we find the conclusions reached from 

 studies on the wieghts of yolks, and on yolk analyses, fully 

 confirmed by a method in which the error involved in the de- 

 termination is wholly negligible. The most accurate method 

 for the study of the storage metabolism of male and female 

 producing ova give too the results most consistent with the 

 breeding data. In other words, we could say, if we wished to 

 make merry with our colleagues, the cytologists, that we here 

 get closest to the facts of sex when we burn our chromosomes! 



The energy values obtained from the burned yolks, permit 

 an indirect comparison of the water values of the male- and 

 female-producing eggs of the clutch. Such a comparison in- 

 dicates, as in the chemical analyses, a higher percentage of 



9 Professor Whitman has observed that the very first egg in life or of the 

 season is more likely to throw a. female than is the first of the clutch of the imme- 

 diately succeeding clutches. 



