PHYSIOLOGY OF REPRODUCTION IN DOMESTIC FOWL. 6 1 



normally a yolk is ovulated into the mouth of the oviduct and 

 passes down the duct, receiving the chalazal layer, chalazae, 

 albumen, shell membrane and shell. The egg remains in the 

 oviduct several hours after the shell is formed. In the case of a 

 few birds which were laying every day a second yolk has been 

 found in the upper part of the oviduct while there was still a 

 hard shelled egg in the shell gland. These birds were killed 

 after they had gone on the nest but before they had laid. That 

 is, when birds are laying at daily intervals two eggs may be nor- 

 mally present in the duct at the same time. In order that two 

 eggs may be separate single-yolked eggs it is only essential that 

 the second does not overtake the first. If the two eggs keep 

 moving toward the cloaca the time between successive ovulations 

 may be somewhat reduced without causing any form of doubling 

 of the egg. What happens is a reduction in the time between 

 the laying of the eggs. Ordinarily the period between two eggs 

 of a clutch is somewhat more than 24 hours. However, some 

 of the best laying birds at the height of their reproductive period 

 lay in less than 24-hour periods. For several days they may lay 

 somewhat earlier each day than on the preceding day. 



One egg every day is the maximum normal egg production. 

 Occasional cases have been reported where two eggs were pro- 

 duced at different times during the same day. Most such cases 

 do not bear- critical investigation. For example, at this and 

 other poultry plants where trap-nests are used, a bird which is 

 already credited with an egg on that day is sometimes found 

 apparently to have laid again. The probability that the bird 

 has actually laid two eggs is much smaller than the probability 

 that the poultryman misread the first band number or some other 

 slip occurred. Unless there is some independent check the 

 evidence cannot be accepted. Such a check was possible in 

 several such cases at this plant. One may be mentioned here. 

 The eggs of bird No. 77 iD were being saved for incubation and 

 each was marked with the bird number when it was taken from 

 the trap-nest. Therefore, when the second egg was taken from 

 the nest on May 19, 1908, the first egg had not been mixed with 

 the eggs of other birds. The resemblance between the two eggs 

 was sufficient to make it certain that the same bird had produced 



