DWARF EGGS OF DOMESTIC FOWL. 299 



IV. The Interrelation of the Dimensions Shape and 

 Weight of Each Class of Dwarf Eggs Compared to the 

 Same Relations in Normal Eggs. 



We have seen that the dwarf eggs of each group vary 

 greatly in each dimension and in weight and shape. We may 

 now consider the correlation in the variation of the several 

 characters in prolate spheroidal dwarf eggs of each class. 



The correlations studied are length with breadth, breadth 

 with weight, length with weight, in;dex with weight, yolk 

 weight with egg weight and yolk weight with albumen weight. 

 On account of the small number of dwarf eggs of known yolk 

 weight the correlations involving yolk weight were calculated 

 directly from the data. In the case of the other pairs of 

 characters the usual correlation tables were made for each class 

 of dwarf eggs. 



Table 3 shows the correlation coefficients with their probable 

 errors and also similar coefficients for normal eggs. 



From Table 3 the following points may be ncted : 



1. In each class of dwarf eggs the correlation between the 

 two dimensions is positive and is certainly significant. That 

 is, a broad dwarf egg is also long and vice versa. The shape 

 of the egg is no doubt determined by the action of the longi- 

 tudinal and circular muscle fibers of the oviduct walls especially 

 during the formation of the egg membrane and shell. The 

 forming egg is a fluid body which tends to take a spherical 

 shape when not under pressure. At the time an egg receives 

 its membrane and shell a normal egg, and almost any dwarf 

 egg, is larger than the normal diameter of the oviduct. It is, 

 therefore, under pressure which tends to elongate it in the 

 direction of the long axis of the duct. The degree of pressure 

 and hence the resulting degree of elongation will depend on 

 (a) the size of the egg compared to the diameter of a cross 

 section of the duct, and (b) the relative tonus of the two sets 

 of muscle fibers of the oviduct wall. A decrease in the tonus of 

 the circular fibers, or an increase in that of the longitudinal 

 fibers, or both, may counterbalance the increase in pressure due 



'Cylindrical eggs appear to show the same relations among themselves 

 as the prolate-spheroidal eggs but the number was too small to deter- 

 mine the significance of the relationship. 



