64 MAYNIE R. CURTIS. 



yolked egg will result. The relation of the two yolks to each 

 other and to the surrounding egg envelopes will depend upon 

 the particular part in the duct above the isthmus ring where the 

 two eggs join, and upon the nature of the processes which bring 

 the two eggs together. 



THE NATURE OF THE DISTURBANCES ix NORMAL EGG PRO- 

 DUCTION WHICH BRING TWO YOLKS TOGETHER IN THE OVIDUCT, 

 AND THE INFLUENCE OF THE PART OF THE DUCT WHERE THEY 

 JOIN UPON THE RELATION OF THE YOLKS TO THEIR ENCLOSING 

 ENVELOPES. 



Parker, 1 in his clear and logical discussion of double hens eggs, 

 explains the cause of double-yolked eggs as the simultaneous 

 discharge of two yolks either from the same or separate ovarian 

 follicles. This is the most simple explanation of the class of 

 double-yolked eggs where the two yolks have apparently passed 

 the entire length of the duct together, as evidenced by the en- 

 closure of the two yolks in a single set of envelopes, beginning 

 with the chalaziferous layer. In such cases the two yolks are 

 often very much flattened together and held by a thin, firm 

 chalaziferous membrane. These yolks have a single set of 

 chalazae and are enclosed in a single envelope of thick albumen. 

 A large number of eggs of this type are produced by the station 

 flock every year. In this group would fall eggs belonging to both 

 of the sub-classes of double-yolked eggs described by Immer- 

 man, 2 that is, those in which the yolks are enclosed in a single 

 vitelline membrane, and also those in which the yolks have separate 

 vitelline membranes. In fact all of the eggs of the first class must 

 fall in this group. The occurrence of two yolks within the same 

 vitelline membrane is, however, very rare among the eggs laid 

 by the station flock. There has indeed been but one such case. 

 In the other apparent cases it was possible by very careful dis- 

 section to remove the chalaziferous layer or chalazal membrane 

 and separate the two yolks. 



While Parker's explanation is sufficient to account for this 

 group of double-yolked eggs it does not account for double- 



1 Loc. cil. 



2 Loc. ci'. 



