SIZE, SHAPE AND PHYSICAL CONSTITUTION OF THE EGG. 1 21 
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 
much 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 weight is apparently least affected by these sea- 
sonal factors. Albumen weight shows very large fluctuations 
which have a decided tendency to repeat themselves in succes- 
sive years and therefore appear to be undoubted seasonal fluc- 
tuations. The fluctuations in shell zoeight are proportionately 
greater than in either of the other parts , but 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 weight 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. 
They may be dtie 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 egg 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. 
