Feb. IS. I9IS Simultaneous Ovulation and Double- Yolked Eggs 381 



Some observations have been made at this laboratory upon the relation 

 of the two follicles occurring in normal ovaries which have furnished the 

 yolks for double-yolked eggs. 



A young pullet, No. 1825 (1913 chick), laid her first egg at 1.30 p. m. 

 on November 20, 191 3. This egg was double-yolked. The bird was 

 killed at 4 p. m. the same afternoon, and the ovary was carefully removed 

 and photographed (PI. LI, fig. i). It was perfectly normal with a gradu- 

 ated series of seven enlarging yolks and two distinct follicles. There 

 was no egg in the oviduct. The bases of the two follicles were separated 

 by about 15 mm. of ovarian epithelium, which was covered with small 

 yolks. 



Another pullet, No. 8053 (hatched in 1913), laid a double-yolked egg 

 at 3.30 p.m. on November 26, 1913. This was her first egg. At 4.35 

 p. m. the bird was killed. There was no egg in the oviduct. Two nor- 

 mal separate discharged follicles were present on the ovary (PI. LI, 

 fig. 2). The bases of the two follicles were quite distinct, although not 

 situated at a great distance from each other. They were supplied by 

 separate arteries from the same branch of the ovarian artery. The 

 ovary was apparently normal in every respect. It contained a series 

 of six enlarging yolks. 



In both these cases the only yolks the bird had ever ovulated were 

 the yolks contained in the double-yolked egg. In each case these yolks 

 were from separate follicles which had separate blood supplies. 



The study of the structure of the egg and of the egg record of the 

 bird has already led to the conclusion that it is not necessary to assume 

 simultaneous ovulation or even an unusually rapid succession of ovula- 

 tions, except in a small percentage of the cases of double-yolked egg 

 production. It, therefore, is important to consider these points in a 

 study of the ovarian relation of the follicles. 



In the two cases just discussed the double-yolked eggs were both of 

 type II — that is, each yolk was inclosed in an envelope of thick albumen 

 and then the two were inclosed in a very thin common envelope of 

 thick albumen. Plate XLVIII, figure i, is a reproduction of a photo- 

 graph of one of these eggs, that of bird No. 1825. The doubling of 

 these eggs had evidently occurred far down in the albumen-secreting 

 region of the oviduct. We should not therefore expect that the two 

 yolks had been simultaneously ovulated. 



The cases in which there is good reason for suspecting simultaneous 

 ovulations are those in which the two yolks are inclosed in a complete 

 set of common envelopes. This shows at least that they have traversed 

 the entire length of the oviduct together. 



An egg of this type was produced on October 18, 1914, by bird No. 

 139M (PI. XLVI, fig. 3). The conniion chalazal membrane has been 

 partly torn away, in order to dcnionslratc that the two yolks have 

 separate vitelline membranes. The bird laid a normal egg on October 



