DWARF EGGS OF DOMESTIC FOWL. 297 



lindrical dwarf eggs the form of the nucleus was not noted. 

 However, in a few pronounced cases it was noted that the 

 nucleus of coagulated fibers of albumen was drawn out in a 

 line parallel to the long axis of the egg. In the prolate sphe- 

 roidal eggs the nucleus is of globular form. That is, its shape 

 is comparable to the shape of a normal yolk. All the eggs 

 with small formed yolks- were of the prolate spheroidal type. 

 It seems probable that the form of the stimulating nucleus 

 is one of the factors in determining the shape of the egg. 



A comparison of the mean indices shows, first, that cy- 

 lindrical dwarf eggs are longer in proportion to their breadth 

 than are normal eggs, while prolate spheroidal eggs are pro- 

 portionately shorter, and second, that dwarf eggs with small 

 yolks are nearer the shape of normal eggs than are dwarf eggs 

 without formed yolks. 



It has been noted that indices for dwarf eggs with small 

 yolks are higher than those for normal and lower than those 

 for other prolate spheroidal eggs. The order for the value 

 of index is thus the reverse of the order for the size characters. 

 Later it will be shown that within each group of dwarf eggs 

 the index is negatively correlated with weight. In earlier 

 investigations 8 it has been shown, first, that the indices for 

 multiple yolked eggs lie below the range of variation for the 

 indices of normal eggs and, second, that within the normal 

 eggs of an individual the index is negatively correlated with 

 weight. The results from the study of dwarf eggs therefore 

 extend the former evidence that the smaller the egg the broader 

 it is in proportion to its length. Two factors may be working 

 together to produce this negative correlation between index 

 and weight. First, the greater the long diameter of the nucleus, 

 be it yolk drop, normal yolk, or two or three yolks in tandem, 

 the longer will be the area of oviduct stimulated at the same 

 time and, second, when a plastic body is forced (by peristalsis) 

 through an elastic tube the tube will offer more mechanical 

 resistance to the passage of a large than a small body. The 

 oviduct will therefore exert a greater elongating pressure on 

 a large than on a small egg. This mechanical factor is probabl} 

 of great importance in determining the shape of the egg. 



8 Curtis 1914 a and b. Loc. cit. 



