Feb. IS, 191S Simultaneous Ovulation and Double- Yolked Eggs 385 



Type III. — Double-yolked eggs in which the j'olks have entirely 

 separate thick albumen envelopes but a common egg membrane and 

 shell. 



(3) Of the eggs studied 16.03 per cent belonged to type I, 70.99 per 

 cent to type II, and 12.98 per cent to type III. 



(4) A large series of double-yolked eggs show all gradations within 

 and between these groups. 



(5) The most probable interpretation of this phenomenon is that the 

 two components unite at any level of the oviduct from the funnel mouth 

 to the isthmus ring. 



(6) The conclusion that the union of the component eggs occurs 

 indiscriminately at all levels of the oviduct is strongly supported by the 

 fact that the percentage of eggs of each type is closely porportional to 

 the percentage of the portion of the duct in which the union of two eggs 

 would give double-yolked eggs of that type. 



(7) In 36.44 per cent of t"he double-yolked eggs the ovulations which 

 furnished the two yolks must have been separated by an abnormally 

 short interval, since a normal egg had been laid on the preceding day. 



(8) An examination of the egg structure, however, shows that the two 

 yolks have passed the entire length of the duct together in only 16.28 

 per cent of the cases in which the ovulations are knowii to have been 

 usually rapid. 



(9) While a heightened rate of fecundity may result in the production 

 of an egg of any of the three types, 68.75 per cent of the eggs of type III 

 are single eggs. It seems probable that many of them have resulted from 

 the delay of the first egg in the oviduct. 



(10) The ovary of each pullet which had just laid a double-yolked egg 

 as her first egg contained two normal separate follicles which had separate 

 blood supplies. In these cases, however, the doubling of the egg had 

 occurred near the end of the albumen-secreting region. 



(11) In a case in which there was evadence from the structure of the 

 egg that the two yolks had passed the entire length of the oviduct to- 

 gether the two follicles were also quite distinct, with separate blood 

 supplies. 



(12) This, together with the fact that in only a small percentage of 

 double-yolked eggs is there any evidence of simultaneous ovulation, 

 indicates that the fusion of follicles and a resulting common blood supply 

 is by no means the usual cause for the production of a double-yolked egg. 



(13) A simple normal follicle furnished the yolk with two germ disks; 

 hence, the fusion of the oocytes (if this was the origin of the two germ 

 disks) must have occurred before the formation of the follicle. 



