CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF 

 THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD 

 COLLEGE. E. L. MARK, Director. No. 173 



DOUBLE HENS' EGGS 



G. H. Parker 



The presence of an additional yolk or of a second more or less 

 perfect egg in a hen's egg, though not an unusual occurrence, 

 is rare enough to excite the attention of those interested in natural 

 phenomena and has been a matter of record since the time of 

 Aristotle. A recapitulation of the early instances of this kind 

 has already been given by Davaine ('61), who has also added 

 much to our knowledge of double eggs. The following account 

 contains a description of five such eggs which have come to the 

 writer's notice in the past few years and present certain features 

 worthy of record. 



Of these eggs the first to be described was laid 26 June, 1905, 

 by a hen belonging to Mrs. Prince Stuart of Wood's Hole, INIass. 

 I am indebted to IMr. A. S. Pearse for the opportunity of examin- 

 ing it. The egg was unusually large, its major axis measuring 

 74 mm., its minor 55 mm. In form it was not unlike a normal 

 egg except that the point was less certainly distinguishable from 

 the butt than is commonly the case. The shell was almost white; 

 near the poles its surface was smooth, but about its equator there 

 was a broad band of unusual roughness. Within was a normal 

 shell membrane inclosing a single mass of albumen containing 

 two yolks. These lay one toward the butt, the other toward the 

 point of the egg. The one toward the butt was approximately 

 spheroidal with its major axis at right angles to that of the whole 

 egg. It measured 34 mm. by 30 mm. The yolk nearer the point 

 was smaller than the other one, by which it was indented on thr 

 side away from the point. It measured 21 mm. by 27 nun., and 

 its major axis was also at right angles to that of the whole egg. 



