378 Journal of Agricultural Research voi. in, no.s 



third type and the comparatively long portion where the union of two 

 eggs could result in an egg of the second type are obviously in accord 

 with the observed percentage of the eggs of each type. 



THE QUESTION OF THE SIMULTANEOUS 0\XaATION OF THE TWO 

 YOLKS OF A DOUBLE- YOLKED EGG 



On purely theoretical grounds Parker ' explains the origin of double- 

 yolked eggs as the "simultaneous or almost simultaneous" discharge of 

 two yolks from the same or separate follicles. He suggests that prob- 

 ably when the two yolks are inclosed in the same vitelline membrane 

 they come from the same follicle, but that when they are in separate 

 membranes the}- are probably from separate follicles. 



Glaser - suggests that it is not necessary to assume simultaneous ovula- 

 tion in the case of the two yolks of a double-yolked egg, since the first 

 yolk may remain in the infundibulum until the next normal ovulation. 

 The present author ■'' has further suggested, first, that this delay of the 

 first egg may occur at any level of the duct anterior to the isthmus ring; 

 second, that the first egg may be moved back up the duct by antiperi- 

 stalsis; and, third, that a yolk ovulated into the body cavity may be 

 later picked up by the funnel and inclosed with its successor in a double- 

 yolked egg. 



It is probable that double-yolked eggs arise from some or all of these 

 causes. However, as was pointed out in the previous paper,'' at least 

 an abnormally close succession of ovulations is necessary to account for 

 a daily succession of double-yolked eggs or of double-yolked eggs laid after 

 a series of normal daily eggs. 



No bird belonging to the flock of the Maine Experiment Station during 

 the last six )ears has produced double-yolked eggs on successive days, 

 but a large number of fowls have produced double-yolked eggs within 

 a series of normal daily eggs. For example, fowl No. 2K produced a 

 double-yolked egg as the seventh egg of a lo-egg clutch. No. 37M one 

 as the sixth egg of a 1.3-egg clutch, and No. 306K produced double-yolked 

 eggs both as the second and fourth eggs of the same 6-egg clutch. In 

 fact, in 43, or 36.44 per cent, of the 118 cases on which we have complete 

 data the bird which produced a double-yolked egg had laid a normal 

 egg on the preceding day. In these cases it seems certain that the period 

 between ovulations must have been much shorter than the normal period. 

 Further, in 17, or 14.40 per cent, of the 1 18 cases the bird laid normal eggs, 

 on both the preceding and following days. In these cases the evidence 

 for a heightened rate of fecundity is unmistakable, although the ov^ula- 

 tions which furnished the >oIks for the double-yolked egg may not have 

 been simultaneous. 



'Parker, G.H. Double hens' eggs, /n Amer. Nat., v. 40, no. 469, p. ij-as, i 6k. 1906. Bibliography, 

 p. »J-3S 

 ' Glaser, Otto. The oriRiii of double-yolked eggs. In Biol. Bui., v. 24. no. 3, p. 175-186. 1913- 

 ' Curtis, M. R. Op. cit. 



