A DOUBLE HEN'S EGG 1 



DR. J. THOMAS PATTERSON, 

 University of Texas 



Double hens' eggs have always attracted much at- 

 tention and the literature covering the records and de- 

 scriptions of the various kinds has become extensive. In 

 a comparatively recent paper published in this journal, 

 Parker 2 has reviewed the main contributions to the sub- 

 ject and from a consideration of these, together with his 

 own observations on five double eggs, has been led to the 

 conclusion that at least two factors are involved in the 

 production of such eggs. According to him, double-yolk 

 eggs are produced when there is a simultaneous dis- 

 charge of two yolks from the ovary, whether these are 

 derived from a single follicle or from two separate fol- 

 licles ; while inclosed eggs may be the product of a normal 

 ovary and probably are produced through the abnormal 

 action of the oviduct, "in that a yolk normally supplied 

 by the ovary may be abnormally covered, retained and 

 inclosed in another egg. ' ' Parker therefore classifies the 

 factors concerned in the formation of double eggs as 

 ovarian and oviducal. Three types of double eggs result 

 from the action of these two factors: (1) those in which 

 the yolks have been derived from an abnormal ovarv but 

 have traversed a normal oviduct, (2) those produced by 

 an ovary and an oviduct both of which have functioned 

 abnormally, (3) and those in which the yolks have come 

 from a normal ovary but have passed through an abnor- 

 mal oviduct. 



The egg described in the following pages clearly be- 

 longs to the third type, and since it possesses certain 



1 Contributions from the Zoological Laboratory of the University of 



54 



