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



In cases of general peritonitis accompanied by visceral adhesions, 

 slight superficial adhesions are sometimes found between the follicles 

 containing hardened yolk. These follicles could never produce normal 

 yolks. 



DESCRIPTION OF A FUSION OF YOLKS WHICH MAY HAVE ARISEN FROM 



A FUSED FOLLICLE 



A small egg weighing only 19.88 gm. was laid on October 19, 1913, 

 by bird No. 19K. This egg contained the double yolk shown in Plate 

 XLVI, figure 2, and weighed only 1.45 gm. Neither part had a visible 

 germ disk. The vitelHne membranes were fused at the point of contact 

 and there was a communication between the cavities of the two yolks, if 

 they were actually separate yolks. The bird had been laying normal 

 eggs and continued to do so. Why this very immature pair of yolks 

 was ovulated is difiicult to understand. Since the bird was not killed, 

 the nature of the follicle which furnished them is not known. 



This and the preceding case are the only ones which have come under 

 our observation in which the two yolks were inclosed in a common 

 vitelline membrane. 



CONCLUSIONS 



The various kinds of evidence given in this paper lead to the con- 

 clusion, first, that double-yolked eggs sometimes represent a heightened 

 rate of fecundity and sometimes an abnormally low physiological tone 

 of the oviduct; second, that, even in cases in which the rate of fecundity 

 is high, the ovulations are not always simultaneous; third, from the above 

 it is apparent that the production of a double-yolked egg can seldom be 

 explained as a result of simultaneous ovulations; and, fourth, in cases 

 in which we have the best of reasons for suspecting simultaneous ovula- 

 tions, the two follicles may be quite distinct. 



It seems quite possible that a heightened rate of fecundity may result 

 in every conceivable shortening of the period between ovulations con- 

 sistent with the daily rhythm in the general physiological activities of 

 the bird. Whether it results in the formation of a double-yolked egg is 

 no doubt determined by the actual length of the period and the following 

 response of the oviduct. 



SUMMARY 



(i) Double-yolked eggs with normal separate yolks may have all the 

 egg envelopes common to the two yolks, or they may have some separate 

 and some common envelopes. 



(2) They may be classified with reasonable accuracy into three groups: 



Type I. — Double-yolked eggs having the entire set of egg envelopes 

 common to the two yolks. 



Type II. — Double-yolked eggs having separate chalaziferous layers but 

 all or part of the thick albumen common to the two yolks. 



