1 82 MAYNIE R. CURTIS. 



4. When a yolk is present in the including egg it always lies 

 toward the blunt end, while the included egg occupies the 

 pointed end. 



These facts indicate that a normal or a dwarf egg which has 

 passed through the duct as far as the isthmus (when the in- 

 cluded egg is only membrane covered) or shell gland (when it 

 has a hard shell) may be returned up the duct without reversing 

 the poles of its long axis. Somewhere, usually in the albumen 

 region, 1 the direction may again be reversed. If the succeeding 

 egg is already forming in the duct the egg which has been forced 

 back lies in the duct posterior to this. As the forming egg 

 completes itself enclosing its predecessor the enclosed egg will 

 of necessity lie in the pointed end and the extent that it is im- 

 bedded within the albumen of the enclosing egg will depend on 

 the level of the duct where the two eggs unite. If there is no 

 second egg in the duct the egg which has been returned may 

 stimulate the duct to the secretion of the egg envelopes. 



The sixteen double, or enclosed eggs which we have had the 

 opportunity of examining include specimens which show many 

 interesting peculiarities. They will, therefore, be described 

 individually. They may, however, be classified according to 

 their general structure into (i) double eggs with the enclosing 

 egg a normal egg and (a) the enclosed egg also normal, or (b) the 

 enclosed egg a dwarf egg; and (2) double eggs in which the 

 enclosing egg does not contain a yolk but is simply a set of egg 

 envelopes enclosing (a) a normal egg, or (b) a dwarf egg. 



I. DOUBLE EGGS IN WHICH THE ENCLOSING EGG is A NORMAL 



EGG. 



This group includes specimens I to 5. 

 (a) The Enclosed Egg is Also a Normal Egg in Specimens I and 2. 



Specimen i (Plate I) was produced at the Maine Station 

 poultry plant. The external appearance of this egg was that 

 of a large membranous sac distinctly pointed. At the blunt end 



1 Gruvel (7) describes a case where the included egg lies between the egg mem- 

 branes of the including egg indicating that the returned egg came upon its successor 

 in the isthmus instead of within the albumen region, as in all the other cases known 

 to the author. 



