STUDIES ON THE CELLS OF CATTLE. 



305 



sex-limited manner similar to the horns in sheep as discussed 

 by Wood ('05) and the rudimentary mammae in swine as reported 

 by Wentworth ('16)." 



TABLE I. 



RESULTS OF NINE POSSIBLE MATINGS OF AYRSHIRE CATTLE. 



The simple Mendelian scheme of inheritance is quite common 

 in cattle but, to my knowledge, this is the only case of sex-limited 

 inheritance reported in this animal ; nevertheless, it is significant, 

 especially in view of our knowledge of the relation between this 

 scheme of inheritance and the sex-chromosomes in many other 



species. 



XI. THE FREE-MARTIN. 



The case of the free-martin, the female of two-sexed twins in 

 cattle, is well known to animal breeders to be perfectly sterile 

 although rarely such females are perfectly normal. I do not wish 

 to enter upon a discussion of this subject here for it is a big 

 problem in itself. However, I wish to call the attention of 

 animal husbandmen, who are not in position to keep in touch 

 with all of the zoological literature, to the extensive and most 

 painstaking piece of research on the free-martin by Dr. Frank R. 

 Lillie ('17). In this connection I might also call attention to his 

 article on sex-determination and sex-differentiation in mammals 

 (Lillie, '17). 



XII. SUMMARY. 



i. Thirty-seven chromosomes occur in the spermatogonia. 

 One, the sex-chromosome, is distinctly larger than the others. 



