REPRODUCTION IN THE DOMESTIC FOWL. 2OI 



the egg membrane was cut and stripped off the clean normal 

 vitelline membrane was exposed. This egg must have passed 

 through the albumen region of the duct without receiving any 

 perceptible quantity of albumen. Whether this was due to 

 exhaustion of the albumen glands or to a rapid passage of the 

 yolk or to some other cause is not known. Evidently under 

 certain conditions the albumen glands do not respond to their 

 normal stimulus even when passing in the normal direction. 

 A failure of the albumen glands is not necessarily accompanied 

 by a failure of the membrane-secreting glands of the isthmus. 

 This egg evidently overtook the normal egg after it had received 

 its egg membrane but before any shell was formed. 



In the other case an apparently normal bird laid an egg which 

 consisted of a normal yolk surrounded by albumen but without 

 either membrane or shell. That is, the membrane- and shell- 

 secreting glands failed to respond to their noimal stimulus. 

 In this case also the cause for this failure is not known. 



In spite of what seems to be a general rule that including egg 

 envelopes are formed only during a downward passage of the 

 egg, three cases are known in which it is possible that the glands 

 of the isthmus may have been stimulated to the secretion of an 

 egg membrane by an egg passing up the duct. Specimen 9 was 

 a hard-shelled egg surrounded immediately by an egg membrane 

 and w r as found in the upper albumen-secreting region of the 

 oviduct. As previously suggested, this may have received the 

 egg membrane when passing up or it may have been returned 

 from the lower albumen-secreting region to the isthmus and 

 then again been forced up the duct to the position in which it 

 \vas found . However, it was more than half way up the albumen- 

 secreting region and had not yet received any albumen. Also 

 two of the double eggs found in the body cavity of the bird with 

 the congenitally closed oviduct had an egg membrane closely 

 surrounding the enclosing egg. In either of these cases the en- 

 closed egg may have received the membranes going up or it may 

 have been temporarily moved caudad from the lower albumen 

 region to the isthmus. In either of these cases it is also possible 

 that there had originally been some albumen between the en- 

 closed egg and the enclosing membrane which had been absorbed. 



