134 MAINE AGRICULTURAL EXPERIMENT STATION. I914. 
The shape of the egg is almost certainly due to the interac- 
tion of the two layers of muscle fibers in the oviduct walls." 
The inner layers of fibers is circular, that is they pass around 
the duct. The outer layer is longitudinal and somewhat spiral 
and extends into both the dorsal and ventral ligaments. Fur- 
ther work on the physiology of these muscles is necessary to 
determine the exact way in which they act. From their posi- 
tion and from observed activities of the duct it seems that the 
contraction of the circular fibers contract the duct and move 
the egg forward. The contraction of the longitudinal fibers, 
which have a somewhat spiral course, expand the duct, dimin- 
ishing the resistance to the passage and also give the egg the 
spiral motion. If the resistance is slight, i. e., if the contrac- 
tions are so timed that the duct ahead of the egg is expanded 
at the time of the contraction of the circular fibers behind, the 
egg will be long, narrow and pointed. On the other hand, if 
the resistance is great the egg will be short and broad. 
The individuality of the eggs of a bird in respect to shape 
must be due to an individuality in the coordination of these 
two sets of muscle fibers and similarily the variation must be 
due to a variation under different conditions in the degree of 
coordination. 
Breadth is more closely correlated with weight of the whole 
egg or with the weight of any of the parts than is length. This 
may be explained by the assumption that the larger the egg 
(beginning with the yolk) the greater the resistance to its pas- 
sage and hence the broader it will be in proportion to the actual 
weight. This may be simply the mechanical effect of a larger 
body passing through the elastic tube or it may be due to an 
unequal increase in the effective stimulation of the two sets of 
muscle fibers. 
General Summary. 
This paper is an analysis of the normal variations in the size, 
shape, and physical constitution of the eggs of the domestic 
$ 'Curtis, M. R. The Eigaments of the Oviduct of the Domestic Fowl. 
Ann. Rept. 'Me. Agr. Expt. 'Sta., 1910, pp. 1-20. 
Surface, F. M. The Histology of the Oviduct of the Domestic Hen. 
Ann. Rept. Me. Agr. 'Exipt. Sta., 1912, pp. 395-430. 
