io28 Journal of Agricultural Research vol. vi,n . 25 



This part of the egg had normal chalazse and thick and thin albumen. 

 The other part, which filled the small portion of the shell, contained a drop 

 of free yolk surrounded by a thick albumen envelope, which was quite 

 distinct from the albumen of the large part of the egg. No thin albumen 

 was present in this part of the egg. The egg had been opened by cutting 

 and lifting off an elliptical piece of the large part of the shell. When the 

 egg was turned out through this opening, only the large part came out. 

 It was then seen that an incomplete shell membrane separated the two 

 components. 



This egg is analogous to the type of double-yolked eggs where the 

 doubleness is visible externally by a depressed ring around the shell, 

 and where internally there is a fold of shell membrane projecting into 

 the deepest part of the furrow. In such double-yolked eggs the thick 

 albumens, are entirely separate. It has been pointed out by Curtis (5) 

 that such an egg must come about from the union of two eggs while the 

 first egg is entering the isthmus, since the formation of the egg membrane 

 is a discrete process taking place immediately when the egg passes the 

 isthmus ring. 1 



The compound egg described above evidently represents the union 

 of a dwarf and a nearly normal egg at this point in the duct. The point 

 of peculiar interest is that the yolk for the two parts of the egg seems 

 to have come from the same normal yolk. The fact that the small 

 component is situated at the end which would have been the pointed 

 end of the larger part had it formed a single egg suggests that the dwarf 

 egg preceded the normal egg through the duct. It is conceivable that 

 during ovulation the yolk membrane was slightly ruptured and that a 

 drop of free yolk entered the duct ahead of- the main body of the yolk. 

 While this seems the most probable explanation of the phenomenon, 

 the shape of the egg may have been modified by the presence of a dwarf 

 egg following. In this case the yolk may have been ruptured either be- 

 fore or after ovulation and a drop left behind may have stimulated the 

 formation of the dwarf egg. 



The bird which produced this compound egg succumbed to roup four 

 days after this egg was laid. She laid a normal egg the day before she 

 died and at autopsy a normal, soft-shelled egg was found in the shell 

 gland. The reproductive organs were in normal active condition. 



Two other compound eggs where one component was a dwarf egg have 

 been produced at the station plant. In neither of these cases was there 

 any external evidence of doubling. The eggs were about as broad as the 

 average egg of the individual, but were perceptibly longer (in one case 

 13 mm.), so that they appeared very long and narrow compared to the 

 other eggs of the birds. There was also no folding in of the egg membrane 



1 The fact that when an egg is entering the isthmus as much and only as much of it as has passed in is 

 covered with membrane was first noted by Coste in 1874. and has since been observed by many investi- 

 gators, including the authors (15, p. 106). 



