Diseases of the Reproductive Organs 277 



be inclosed in the same egg membrane is that they enter 

 the membrane secreting portion of the oviduct together. 

 There are at least three possibilities besides 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 abnormally 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 

 simultaneous ovulations ; but in about a third of the cases of 

 double-yolked eggs 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 they 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 pro- 

 duced double-yolked eggs showed that each of the two 

 yolks was discharged from a normal separate follicle exactly 

 as are the yolks of successive single-yolked eggs. 



From these recent studies of double-yolked egg produc- 



