CHAPTER V 

 TWINNING IN RUMINANTS— THE FREEMARTIN 



All ruminants produce habitually but one offspring 

 at a birth, but in several species (probably in all) two 

 or more offspring occasionally are born at once. Such 

 offspring are naturally spoken of as twins or triplets. 

 Twinning in cattle and in sheep has received consider- 

 able attention because of the economic aspects of the 

 case; if it should prove to be an inherited trait, it 

 would be a distinctly advantageous character to en- 

 courage by breeding. 



Less attention has been paid to twinning in wild 

 ungulates; that the phenomenon occurs in the deer is 

 proved by the beautiful picture of a doe with twin fawns 

 published some years ago in the National Geographic 

 Magazine.' The twin fawns are remarkably ahke, and 

 if one were to judge by appearances alone, he might be 

 inchned to class them as monozygotic or duplicate twins. 

 Such unsupported evidence would, however, scarcely 

 justify the conclusion. 



At the present time I have no reliable evidence of 

 twinning in horses, but it is highly probable that this 

 group offers no exception to the general rule that all 

 mammals normally producing but a single offspring 

 at a birth may have twins. There are certain evidences 

 of a kind of twinning in swine involving the formation 

 of double monsters. That separate monozygotic twins 



^National Geographic Magazine, XXIV (1913), 762. 

 9S 



