Vol. XLIV. February, TQ2 j. No. 2. 



BIOLOGICAL BULLETIN 



SUPPLEMENTARY NOTES ON TWINS IN CATTLE. 



FRANK R. LILLIE, 



Zoological Laboratory, University of Chicago. 



Since the publication of my previous papers on the free-martin 

 (1916, 1917) more material has been slowly accumulating. The 

 additional data have confirmed and strengthened my former con- 

 clusions, and they also include some observations of a certain 

 amount of intrinsic interest. The present paper, therefore, is a 

 series of supplementary notes on twinning in cattle, with comments 

 on more recent literature. 



1. Cases Where the Female of Two-sexed Pairs is Normal. 

 In my previous paper I concluded that the free-martin is zygoti- 

 cally female, and that its intersexual condition is due to action of 

 the blood of the male twin through anastomosis of the foetal blood 

 vessels which develops very early; Keller and Tandler (1916) 

 came to the same conclusion as the result of entirely independent 

 studies. This theory receives a crucial test in those relatively rare 

 cases of two-sexed twins in which no such anastomosis develops, 

 for in such cases the reproductive system of the female should be 

 normal. In my previous paper I reported three cases of a normal 

 female twinned with a male out of twenty-four pairs of two-sexed 

 twins. The records of the first two cases (Nos. 8 and 9) were, 

 however, incomplete, and the question of vascular anastomosis was 

 not fully investigated because they were received before any 

 theory on the subject was developed. They were, however, con- 

 sistent with the above interpretation, for it was recorded in the 

 notes made at the time of collection that the connection between 

 the two chorions was narrow; presumably there was no vascular 

 anastomosis. The third case (No. 40) was, however, a perfect 

 test case in every respect ; there was a corpus luteum in each 



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