126 MAINE AGRICULTURAL EXPERIMENT STATION. I914. 
in size from the first egg. The first egg of a new clutch is 
larger than the last egg of the preceding clutch. There are a 
few exceptions to this especially where a litter begins with a 
long clutch. 
The fact that in general the eggs laid on successive days de- 
crease in size while after a day or two on which no egg is 
produced the egg size increases seems to indicate that there 
is either an exhaustion of material available to elaborate into 
the various egg parts or that there is a fatigue of the reproduc- 
tive organs which causes a decrease in the amount of material 
elaborated. A variation in the supply of available materials 
or a variation in the physiological tone of the organ would ac- 
count for the cases of unusual size relations between succes- 
sive eggs. 
It has now been shown that the variation in egg weight is 
related to the age of the bird, the season of the year, the state 
of health and the rate of egg production. 
The weight of all the eggs and egg parts for the individual 
birds for two years furnish material to test Pearl’s* (’07) 
“second law of growth” i. e., that the variability of succes- 
sively produced like parts decreases with the number of such 
parts produced. If this law was operating during the produc- 
tion of successive eggs the magnitude of the fluctuations in egg 
weight would decrease with the number of eggs laid. The dia- 
grams described on page 125 show that the fluctuations in 
egg weight and weight of each of the egg parts are as large 
at the end of the second as at the beginning of the first year. 
It is evident then that this law does not hold for the variation 
in weight of successive eggs. Pearl t (’09) found no evidence 
that this law was acting in regard to the shape of the eggs of 
a fowl on which he studied regulation in shape. 
This section of the paper has shown that the weight of any 
part of a bird’s egg depends, first upon the hereditary constitu- 
tion of the bird, second her physical constitution or state of 
health, third, her stage of development, fourth, the season of 
the year, and fifth, the position of the egg in its clutch and 
* Pearl, R. Loc. cit. 
f Pearl, R. Loc. cit. 
