126 MAINE AGRICULTURAL EXPERIMENT STATION. I9I4. 



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 H'eight of any 

 part of a bird's egg depends, first upon the hereditary constitu- 

 tion of the bird, second her physical constitutioii 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. 

 t Pearl, R. Loc. cit. 



