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 somewha^t spiral 

 and extends into both the dorsal and ventral ligaments. Fur- 

 ther work on the physiology of these muscles is necessary to 

 determine the exadt 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 similarity the variation must be 

 due to a variation under different conditions in the degree of 

 coordination. 



Breadth is more closely corrected 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 efifect 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 



t Curtis, M. R. The Ligaments of the Oviduct of the Domestic Fowl. 

 Ann. Kept. Me. Agr. Exipt. 'Sta., 1910, pip. 1-30. 



Surface, F. M. The Histology of the Oviduct of the Domestic Hen. 

 Ann. Rept. Me. Agr. Expt. Sta., 1912, pp. 395-430. 



