1 14 MAINE AGRICULTURAL EXPERIMENT STATION. I 9 I 4 . 
seasonal fluctuations which will be discussed later ; but with 
very few exceptions the eggs of the second year are decidedly 
larger than the eggs of the corresponding months of the first 
year. That is the eggs of a bird continue to increase in weight 
with the increased maturity of the bird at least up to the end 
of the second laying year. After the beginning of the first 
breeding season the increase in weight is much slower than dur- 
ing the few months which precede. 
The weight of the egg is made up of the weight of the three 
parts albumen, yolk and shell. Each of these parts are also 
variable in weight. In fact, each is more variable than the 
weight of the whole egg. 
A study of the progressive change in each of these parts can 
be made in a manner similar to the above study of egg weight. 
The monthly mean yolk weights show ever more uniformily 
than, the weight of the whole egg that the weight increases 
rapidly to the beginning of the first breeding season and from 
that time on more slowly. The yolk weight shows the seasonal 
fluctuations shown by the egg weight; but their magnitude is 
smaller. 
The monthly mean albumen weights show a less abrupt rise 
during the first three months and greater seasonal fluctuations 
than the monthly mean egg weights or yolk weights. In gen- 
eral, however, they show an increase in albumen weight with an 
increase in the age of the bird. 
The monthly mean shell weights are larger for the second 
than for the first year but they show a large proportional varia- 
tion which is usually related to the variation shown by the 
other parts but may be independent and in the opposite direc- 
tion. For example during the first three months laying all but 
one of the birds show a decrease in shell weight which is as 
decided as the increase in the weight of the other two parts. 
In order to generalize the study of the increase in the weight 
of eggs and of each of its parts as the bird grows older it is 
desirable to bring together the results of the study on the 
individual birds. 
The birds used in this investigation form a more homoge- 
neous group than is often available for statistical work. They 
were “p ure -bred” in the fancier’s sense and line-bred and were 
within a few weeks of the same age. They had lived under the 
