SPECIAL REPORT FOR YEAR I9I4. 7 



necessary for two yolks to be enclosed in the same &gg mem- 

 brane is that they entered the membrane secreting portion of 

 the oviduct together. There are at least three possibilities beside 

 simultaneous ovulation which may bring two yolks together 

 before they reach this portion of the oviduct. First, the first 

 yolk may be delayed at any level of the duct forward to the 

 point where the egg membrane begins to be secreted ; second, 

 the first yolk may be returned up the oviduct and then come 

 back in company with the second yolk ; and, third, a yolk may 

 be ovulated into the body cavity and picked up by the oviduct 

 shortly before or after the ovulation of another yolk. It is, 

 therefore, unnecessary to assume that the production of a 

 double-yolked egg represents simultaneous or even an abnor- 

 mally rapid succession of ovulations, since any of these delays 

 may have been as long as the normal period between ovulations. 



A study of the structure of the eggs and the egg records of 

 the birds leads to the conclusion that double-yolked eggs do 

 not necessarily represent two simultaneous or even nearly sim- 

 ultaneous ovulations ; but in about one-third of the cases of 

 double-yolked eggs produced at this Station the time between 

 the two ovulations must have been unusually short, since the 

 birds which laid these double-yolked eggs each laid a normal 

 egg on the preceding day. A study of the egg structure of these 

 double-yolked eggs where the time between the ovulations is 

 known to have been abnormally short shows that the ovulations 

 have been simultaneous in only a small per cent of the cases. 

 In fact the two yolks have come together at every level of the 

 duct in front of the beginning of the isthmus. 



A study of the ovaries of birds which had recently produced 

 double-yolked eggs showed that each of the two yolks was dis- 

 charged from a normal separate follicle exactly as are the 

 yolks of successive single yolked eggs. 



From these recent studies of double-yolked egg production it 

 is certain that some individual hens have an inherent tendency 

 to lay double-yolked eggs while a great majority of hens never 

 lay anything but normal single-yolked eggs. A bird with the 

 tendency to double-yolked egg production is more likely to pro- 

 duce double-yolked eggs when she is quite young than later in 

 life. 



