376 Journal of Agricultural Research voi. m, no. 5 



projecting into the albumen at the deepest part of the furrow (PI. XLIX, 

 fig. 2). Although the eggs form a continuous series, they can be sepa- 

 rated with reasonable accuracy into three classes or types: 



Type I. — Double-yolked eggs having the entire set of egg envelopes 

 common to the two yolks. 



Type II. — Double-yolked eggs having all or part of the thick albumen 

 common to the two yolks, but with separate chalazal membranes. 



Type III. — Double-yolked eggs in which the yolks have entirely 

 separate thick albumen envelopes but a common egg membrane and 

 shell. 



RELATION OF THE NATURE OF THE DOUBLING OF THE EGG TO THE 

 SEVERAL FUNCTIONAL DIVISIONS OF THE OVIDUCT 



The most obvious interpretation of the various types of doubling 

 observed in double-yolked eggs is that the two components may come 

 together at any level of the oviduct from the ostium to the isthmus ring. 

 The eggs classified as type I arise when the union of the two yolks occurs 

 in that part of the duct where chalazal membrane is secreted (probably the 

 funnel and funnel neck); type II, when the union is at any level in the 

 albumen-secreting region more than the length of the first egg anterior to 

 the isthmus ring; and type III, when the union occurs while the first egg 

 is passing the isthmus ring. 



Observations of the relation of the egg envelopes were made on nearly 

 every double-yolked egg produced at the plant of the Maine Experiment 

 Station during the past year. Data were collected on 131 eggs with two 

 normal yolks and a common egg membrane and a shell. Only 21, or 

 16. 03 per cent, were united in a common chalazal membrane, showing 

 that they had passed practically the entire length of the oviduct together. 

 In contrast to this, 93, or 70.99 per cent, had separate chalazal membranes 

 but with all or part of their thick albumen common to the two yolks. 

 These eggs showed every possible gradation from two yolks with entirely 

 common thick albumen envelopes to cases where the two component 

 eggs were contained in a very thin layer of common thick albumen. 

 They had apparently come together at every possible level of the duct 

 from a point in the funnel where the chalazal membranes are complete 

 to a point near the lower end of the albumen-secreting region. Seventeen 

 eggs, or 12.97 per cent, had entirely separate thick albumen envelopes. 

 They had evidently come together while the first component was passing 

 the isthmus ring. 



The large proportion of double-yolked eggs with all or part of their 

 thick albumen common to the two yolks is easily explained by the length 

 of the portion of the duct in which they may come together. A photograph 

 of the oviduct opened out to show the various regions is reproduced in 

 Plate L. There is no visible line of demarcation between the funnel 



