Feb. 15. 1915 Simultaneous Ovulation and Double- Yolked Eggs 383 



with two large and apparently normal germ disks (PI. XLVI, fig. i). 

 There was a thin white line visible only part way around the yolk but 

 passing between the two disks and standing out plainly in this region. 

 The size of the yolk, the presence of two germ disks, and this line were 

 the only evidences of doubling. The vitelline membrane was punctured 

 and the yolk removed. The membrane was washed out carefully with 

 salt solution. It contained a single cavity, with no suggestion of doubling, 

 except the slight thickening seen as a white line on the surface of the 

 yolk. The weight of albumen and shell, 44.47 and 7.66 gm., respectively, 

 was comparable to the weight of these parts in a double-yolked egg 

 where the two yolks are separate. 



This egg clearly belongs to the first class described by Immerman ■ in 

 which the two yolks are in a single vitelline membrane. 



The bird which laid this egg was killed at 11 a. m. on the following 

 day. A normal egg weighing 45.81 gm. was in the shell gland. The 

 yolk of this egg was normal, having a single germ disk. It weighed 

 17.7 gm., which is about 59 per cent of the weight of the yolk with the 

 two germ disks. The egg contained as yet only a small amount of thin 

 albumen and no visible shell. It had evidently just entered the shell 

 gland. The contained yolk had without doubt been ovulated the 

 morning of the day the bird was killed, or about 48 hours after the 

 ovulation of the yolk with the two germ disks. The egg would not have 

 been laid until the second day following the one on which the large egg 

 was laid. 



The ovary of this bird is shown in Plate LII, figure 2. Two of the 

 enlarging yolks have been removed, in order to show the follicles. Only 

 ihree large follicles were present. Two of these, A and B, were about 

 the same size, A being somewhat larger. The stalk of the third, which 

 was considerably smaller, is seen at C. Either A or B must have fur- 

 nished the yolk with the two germ disks. This yolk was nearly twice the 

 size of the normal yolk in the oviduct. In the time which elapsed between 

 the two ovulations the follicle which had produced this enormous yolk 

 had been resorbed to practically the size of the one just ovulated. Neither 

 of these follicles, nor in fact any other on the ovary, showed any evidence 

 that it was composed of two fused follicles. If the double yolk arose 

 from the fusion of two oocytes, it seems probable that this took place 

 at a stage earlier than the formation of the follicle. 



The practically double size of the yolk contained in a single follicle 

 but with two germ disks suggests that the germinal vesicle may be an 

 important factor in determining the quantity of yolk deposited within a 

 yolk membrane. 



In the domestic fowl the fusion of follicles in an ovary capable of 

 producing normal yolks must be of rare occurrence. The examination of 

 several hundred ovaries of laying birds has not furnished a single case. 



* Immerman, Ferdinand. Ober Doppcleier bcim Huhn. 43 p., 5 fig. Basel, 1S99. Inaugural Disser- 

 tatiun. 



