riddle: control of sex ratio 339 



water in the male-producing ovum. In addition to these two 

 methods of studying the water values of the two kinds of eggs 

 the value has been obtained direct, by desiccation, on a con- 

 siderable number of samples. The three methods confirm each 

 other. A little later we shall make a further application of the 

 observed facts of higher water values, and of a higher metabo- 

 lism in the male-producing ova. 



Let us now very briefly consider the other kinds of obser- 

 vations that have been made on the series of eggs, from spring 

 to autumn, produced under crowded reproduction by generic 

 crosses, as these are schematically represented in Chart 1. 

 Curves 2 and 3 on that chart represent facts which were first 

 observed by Professor Whitman on these series of eggs. The 

 curve entitled " developmental energy" (No. 2) represents the 

 observed fact that more of the eggs of spring show the capacity 

 to develop than do those of autumn; and by the use of a con- 

 tinuous (not broken) line or curve is indicated the further fact 

 that the first eggs of the clutch bear throughout the season a 

 similar relation (of higher fertility) to the second eggs of the 

 clutch. The curve marked 3 and designated " length of life" 

 tells again of an advantage possessed by the earlier hatched 

 birds, and of a more limited life-term affixed to the hatches, 

 from the later " overworked" eggs. It is probable, moreover, 

 that within the group of clutches giving rise to females only, a 

 longer life-term falls to those birds arising from the first egg of 

 the clutch than from those arising from the second of the clutch. 

 Here, then, as in the preceding curve (2), the smaller eggs of 

 both clutch and season are the eggs which give in their develop- 

 ment the tests of "strength and vigor," while the larger eggs 

 of clutch and season more often display " weakness." 



The data which justify curves 4 and 5 as represented on the 

 chart have already been considered. Of the observations upon 

 which curve 6 is based we shall here say only that in general 

 the weight of the parent bird is greatest at the season when the 

 weights of the yolks being produced are smallest, and that when 

 the largest yolks of autumn are being produced the weight of 

 the parent bird is the smallest of the year. Tables 4 and 5 



