2O2 MAYNIE R. CURTIS. 



In a previous investigation (3) attention was called to the 

 possibility that under certain conditions the return of an egg 

 up the duct may result in the formation of a double-yolked 

 egg. It seems quite possible, that the reversal of the direction 

 of an egg may be more frequent than we have formerly supposed. 

 The result of such a reversal must depend on the state of de- 

 velopment of the egg when the backward motion begins, the ex- 

 tent of the backward movement, the rate of fecundity of the 

 individual bird at the time, etc. For example, if an egg which 

 has not yet received its egg membrane is forced backward toward 

 the funnel but not expelled from the duct and then without 

 meeting its successor moves forward again the only result will 

 be an unusually large amount of albumen. If an egg without a 

 membrane which is moved up the duct but not expelled meets 

 its successor and returns with it through the duct, the result 

 will be a double-yolked egg. While it must be admitted that 

 since the succeeding yolk is not usually ovulated for some 

 hours after an egg has received a membrane, yet yolks are 

 certainly sometimes ovulated at considerably shorter intervals. 

 It is also possible that the tone of the oviduct may sometimes 

 be so low that an egg may remain practically stationary for a 

 time. So soon, however, as the egg receives its membrane it 

 can combine with its successor only as a double egg. Either a 

 normal or a dwarf egg may be returned up the duct and may 

 either be expelled from the funnel into the body cavity or at 

 any level of the duct the direction may again be reversed. If 

 the egg becomes united with its successor it becomes enclosed 

 with it in some common envelopes, the number which are com- 

 mon depending on the level of the duct at which the components 

 unite. If it does not meet its successor it becomes a nucleus 

 around which are formed the envelopes which are normally 

 secreted below the point where the forward direction is again 

 resumed. It thus seems that the formation of a double egg does 

 not involve unique processes, but that this phenomenon results 

 from certain combinations of processes, most of which are the 

 normal processes of egg formation. The abnormal factor the 

 reversal of direction of the egg when of greater extent results 

 in the expulsion of the egg into the body cavity from which it is 



