Il6 MAINE AGRICULTURAL EXPERIMENT STATION. I9I4. 
From this table it is seen that in the case of the flock, as 
in the case of individual birds, the yolk weight increases more 
constantly than the weight of the other two parts or of the 
whole egg. That is it shows smaller irregular fluctuations. 
The flock monthly mean yolk weight increases very rapidly 
at first. The increase in weight is actually greater during the 
first four months than during the next twenty months. The 
yolk weight, however, continues to increase during the second 
year. This suggests that the increase in yolk weight is follow- 
ing a logarithmic curve of the form y=A-\-Bx-\-C log x where 
yz^yolk weight, x— time, and A, B and C are constants. This 
type of curve was fitted as a first trial. 
The resulting curve is 
y— 12.6728 — .0261^+4.5669 log x. 
When the ordinates of this curve are calculated and plotted 
together with the observation curve the smooth curve shows an 
excellence of fit which indicates that the increase in weight of 
the egg yolk in these birds is in fact expressed analytically by 
this logarithmic curve. In other words this shows that the 
mean yolk weight increases with each successive month from 
the beginning of laying at least to the end of the second year 
but the rate of increase diminishes with the successive months. 
The data on which these calculations were based were taken 
from the eggs of birds which began to lay at an age of from 
five and one-half to six and three-fourths months. It is inter- 
esting to know the size of the egg yolks at the beginning of 
laying and the direction and rate of change in yolk weight when 
a bird is older or younger than this at the time she begins to 
lay. For this reason three birds that began to lay February 
23 were added to the individuals under investigation. These 
birds were eight and three-fourths to nine months old, i. e., they 
were from two to three and one-half months older than those 
pullets just discussed. It is not so easy to investigate pullets 
which begin to lay younger, as the Barred Plymouth Rocks, at 
least under the methods of hatching and handling employed at 
this station, rarely lay before they are five months old. We 
are indebted to Mr. Walter Gerald of Unity, Maine, for the 
opportunity to obtain data on the first ten eggs of a pure bred 
Barred Plymouth Rock pullet which began to lay when she was 
exactly three months old and before she had moulted her 
