SIZE, SHAPE AND PHYSICAL CONSTITUTION OF THE EGG. 1 29 
limits to this relationship. When a number of eggs are pro- 
duced in succession each successive egg is smaller than its pre- 
decessor. There is probably either an overdemand on the 
amount of available material or there is a fatigue of the repro- 
ductive apparatus which hinders the formation of the egg parts. 
A study of the interrelation of the different parts of the egg 
is a study of the correlation of the activities of the different 
organs and parts of organs by which they are formed. The 
fact that the oviduct of a bird approaching a period of laying 
enlarges as the yolks enlarge has been long recognized. The 
observations on the domestic fowl at this laboratory agree in 
general with those of Bartelmez * on pigeons. There are 
nevertheless some specific differences between fowls and 
pigeons. In a bird in the non-laying condition the oviduct is 
a small straight tube and there are no oocytes in the ovary 
which contain a perceptible amount of yolk. About the time 
a group of oocytes enters upon the final growth period (when 
they begin to enlarge above 6 mm.) the oviduct begins to en- 
large. The stimulus which initiates these activities in fowls is 
not known. There is no evidence that it is connected with 
mating as has been shown for the pigeon.! The presence of the 
male is certainly not necessary and no behavior on the part of 
a fowl has been observed to indicate that she is physically 
mated with another female or with anything else. Whatever 
the stimulus that starts the reproductive mechanism going, it 
is true that while the first yolk is forming the oviduct enlarges 
to functional size. 
This correlation between the ovary and oviduct is now com- 
monly attributed to the action of the internal secretion of the 
ovary. Bartelmez * states that “interstitial cells of the ovary 
show much greater signs of activity in functioning ovaries 
than do those in ovaries of birds that had not laid for a long 
time.” That the enlargement of the oviduct is due to the in- 
* Bartelmez, George W. The Bilaterality of the Pigeon’s Egg. Jour, 
of Morph., Vol. 23, 1912, pp. 270-310. 
t Harper, E. H. The Fertilization and Early Development of the 
Pigeon’s Egg. Am Jour. Anat., Vol. 3, 1904, pp. 344-381. 
Craig, W. Oviposition Induced by the Male in Pigeons. Jour, of 
Morph., Vol. 22, 1911, pp. 299-305. 
t Bartelmez, G. W. Loc. cit. 
