PHYSIOLOGY OF REPRODUCTION IX DOMESTIC FOWL. 65 



yolked eggs where the two yolks have some separate envelopes. 

 Nor indeed is it the only possible explanation for double-yolked 

 eggs where all the envelopes are common to the two yolks. 



Glaser 1 suggests that a failure of the peristalsis of the duct 

 just below the infundibulum, due either to "a deficiency of 

 substance normally inducing the movements or (to) the sub- 

 normal irritability on the part of the oviduct," might result in a 

 yolk remaining in the upper part of the duct until a second was 

 normally ovulated. The two might then pass down the duct 

 together. Whether or not this ever happens is not known, but 

 it is, certainly, theoretically possible. 



Glaser's second suggestion as to an additional cause for the 

 formation of double-yolked eggs is based upon the case he de- 

 scribes where the laying of double-yolked eggs was "habitual." 

 The suggestion is that in such cases the laying of double-yolked 

 eggs may have a "distinct ovarian basis" which in this case he 

 believes to be the tendency to a secondary fusion of follicles which 

 results in a common blood supply. This seems rather to be a 

 suggestion of the nature of the underlying cause of the syn- 

 chronous maturity and discharge of two or more yolks. The 

 fusion of follicles and a common blood supply may be an im- 

 portant cause for simultaneous ovulations. 



There is, however, one additional possibility for the formation 

 of double-yolked eggs with a single set of egg envelopes. A yolk 

 may be ovulated into the body cavity and remain in that portion 

 of it which is walled off into a sort of ovarian pocket 2 formed by 

 the mesentery, coeca, and air sac wall. It is thus near the mouth 

 of the oviduct. If this free yolk entered the infundibulum just 

 before or immediately after a second ovulation the two yolks might 

 pass down the duct together. A free yolk has never been seen 

 entering the oviduct but many observations of ovulation into 

 the body cavity and the anatomical relation of the infundibulum 

 to the ovary make it necessary to list this among the theoretically 

 possible causes for the presence of two yolks in the duct at the 

 same time. 



1 Loc. cii. 



8 This pocket has been described by the author in a previous paper. Curtis, 

 M. R., "The Ligaments of the Oviduct of the Domestic Fowl," Ann. Kept. Me. 

 -Agr. Exp. Sta., 1910, pp. 1-20. 



