PHYSIOLOGY OF REPRODUCTION IN DOMESTIC FOWL. 8 1 



tripling the weight of yolks does not cause a proportionate 

 increase in the secretion of albumen and shell, nevertheless 

 doubling causes an increase and tripling a still slightly greater 

 increase. This shows that either the glands of the oviduct are 

 not all completely discharged duiing the formation of a bingle- 

 yolked, or even a double-yolked egg, or that under stimulation 

 they elaborate their secretions with great rapidity. 



A COMPARISON BETWEEN THE SHAPE OF SINGLE- AND MUL- 

 TIPLE- YOLKED EGGS OF THE SAME INDIVIDUAL. 



It may be seen from Tables II. and IV. that there is a decided 

 difference in the shape of single- and multiple-yolked eggs pro- 

 duced by the same bird. The multiple-yolked eggs are both 

 longer and broader than the single-yolked eggs, but they are 

 not as broad in proportion to their length. This may be best 



100 breadth 

 seen by comparing the length-breadth index : r ol the 



double-yolked or triple-yolked egg with the mean index for the 

 ten succeeding eggs. In all cases the mean index for the normal 

 eggs is higher, showing that the normal egg is broader in pro- 

 portion to its length. In Table IV. the lowest index for the eggs 

 produced by each bird duang the first year is also given. In 

 every case but one the index of the double-yolked egg is lower 

 than the minimum for all the first year normal eggs. That is, 

 it falls below the noimal variation for the individual. The 

 multiple-yolked egg then is longer in proportion to its breadth 

 than any of the normal eggs of the same individual. 



The yolks pass down the duct in succession, and not abreast. 

 In the complete egg they lie with their common axis in the long 

 axis of the egg. They must, therefore, stimulate the oviduct 

 glands in succession. However, the eggs with two or three yolks 

 are actually broader than those with one. This may be due in 

 part to the fact that the field of stimulation of the two yolks 

 overlaps, but probably the most important factor is the mechan- 

 ical one due to forcing (by peristalsis) a larger plastic mass 

 through an elastic tube, which offers more resistance to the 

 passage of a large than a small body. 



