390 



THE AMERICAN NATURALIST 



[Vol. L 



gradual enlargement. This fact is represented diagram- 

 matically on chart I, and some of the actual figures may 

 be had from the charts dealing with size of offspring 

 (II), with analyses (III), and with calorimetry (IV). 



H U U U % % 



At the same time that this seasonal increase in size of 

 yolks was learned, it also became evident that the eggs 

 of doves and pigeons are dimorphic : That the two eggs 

 forming the pigeon's clutch bear usually-there are ex- 

 eeptions-a smaller yolk in the first, and a larger yolk 

 m the second. Since Whitman had alreadv shown that 



