Vol. XLIL January, 1922 No. i. 



BIOLOGICAL BULLETIN 



IDENTICAL TWINS IN CATTLE? 1 



JOHN W. GOWEX. 



The phenomenon of a sterile, female-appearing animal resulting 

 as a co-twin to a normal male has called attention to the problem, 

 Do identical twins occur in cattle? 



Three lines of evidence are available in answer to this question. 

 The first consists of anatomical evidence, the ovaries of a twin- 

 producing cow during pregnancy. This is the most critical and 

 most desired. The second consists in the study of the normal sex 

 ratios occurring in multiple births of cattle in comparison with 

 those occurring in species where identical twins are produced. 

 The third method consists in a comparison of the color markings 

 of twins of the same or opposite sex. 



In his paper on the freemartin, F. R. Lillie 2 collects data on 

 the condition of the ovaries of cows producing twins. He showed 

 in 22 cases where both ovaries were obtained corpus luteum were 

 present in each. In 1 1 cases where only one ovary was obtained 

 9 had corpus luteum in that ovary. The two pairs of twins whose 

 mothers lacked corpora lutea in the remaining ovary were of the 

 same sex, one pair being males, the other pair females. These last 

 two pair of twins may be identical or monozygotic twins. This 

 appears doubtful, for as the data of Cole presented later will show, 

 the proportion of single ovaries ovulating twice when the other 

 one does not ovulate should not be very far from the proportion 

 indicated by Lillie's data, providing, of course, that one ovary may 

 ovulate twice when the other does not ovulate at all. 



Lillie furnishes other data on the sex ratio of intrauterine twins 



1 Papers from the Biological Laboratory of the Maine Agricultural Experi- 

 ment Station No. 141. 



2 Lillie, Frank R., 1917, "The Freemartin; A Study of the Action of Sex 

 Hormones in the Foetal Life of Cattle," in Jour. E.\-pt. Zool., Vol. 23, p. 

 371-422. 



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