SIZE, SHAPE AND PHYSICAL CONSTITUTION OF THE EGG. 121 



When the monthly mean shell weight is compared month by 

 month with the monthly mean albumen weight many of the 

 same fluctuations will be noted. There is one decided exception. 

 During the first three months shell weight is decreasing propor- 

 tionately more rapidly than the albumen weight is increasing. 

 The fluctuations shown at other seasons are proportionately 

 m.uch greater in shell weight than in albumen weight. 



The variation in weight which is associated with the change 

 in season is to a certain extent similar in the case of each part 

 of the egg. The parts, however, vary greatly in the propor- 

 tional magnitude of the seasonal variations. The difference is 

 so great that the proportion of the parts is altered in different 

 seasons. Yolk zueight is apparently least affected by these sea- 

 sonal factors. Alhunien iveight shows very large fluctuations 

 which have a decided tendency to repeat themselves in succes-^ 

 sive years and therefore appear to he undoubted seasonal fluc- 

 tuations. The fluctuations in shell zveight are proportionately 

 greater than in either of the other parts, hut do not show the 

 same tendency to repeat themselves in the successive years. It 

 therefore seems possible that some of the large fluctuations in 

 shell zceight may be due to some other circumstances than the 

 normal change in season. 



Showing that certain changes in yolk weight and albumen 

 weight are correlated with change in season does not indicate 

 the fundamental cause of these changes. The solution of this 

 problem must be by controlled experiments. Two interpreta- 

 tions suggest themselves, i. The fluctuations may be due 

 to the direct effect of seasonal changes in environment. 2. 

 The}^ may be due to the general changes in metabolic processes 

 which also find expression in the differentiation of a breeding 

 season and a fall molt, and which are probably due in part to 

 environment and in part to heredity. 



In general it seems probable that while the seasonal fluctua- 

 tions in Qgg weight may be to some extent the direct effect of 

 environmental conditions, yet to a much greater extent they are 

 the indirect effect of such conditions. That is they are due to 

 general physiological changes in the individual. 



