382 FRANK R. LILLIE 



My own records of 55 cases of bovine twins, all examined in 

 utero, and their classification determined anatomically without 

 the possibility of error, give 19cfcf':24cf9:ll 99 and 1 

 (no. 49) too young for determination. It will be observed that 

 the sum of the one-sexed classes is 25 per cent greater than the 

 two-sexed class; and the cf cf class is much larger than the 9 9 

 class instead of being equal to it, as it should be if males and 

 females are produced in equal numbers in cattle. The material 

 cannot be weighted statistically because every uterus containing 

 tmns below a certain size from a certain slaughter house is sent 

 to me for examination without being opened." Cole's material 

 shows twice as many female as male pairs, and the two-sexed 

 class is about one-third greater than the sum of the other two 

 classes. I strongly suspect that it is weighted statistically; the 

 possibility of this must be admitted, for the records are assembled 

 from a great number of breeders. But, whether this is so or 

 not, if we add the sterile free-martin pairs of my collection to the 

 male side in accordance with Cole's suggestion, we get the ratio 

 40d'cf:3d^9:ll9 9, which is absurd. And if we take Cole's 

 figures, divide his heterosexual class into pairs containing sterile 

 females and pairs containing normal females according to the 

 expectation, 7 of the former to 1 of the latter, and add the former 

 to his male class, we get an almost equally absurd result (180 

 d" cT: 20 o^ 9 : 88 9 9). On the main question our statistical 

 results are sufficiently alike to show that the free-martin must 

 be interpreted as female. 



Prof. Alexander Graham Bell has kindly furnished me with a 

 catalogue of the lambs born from 1890 to 1914 in his well-known 

 experiments on his Beinn Bhreagh Estate in Nova Scotia from 

 which I have taken all the records of twin births, 139 in number; 



* The great preponderance of the d^cT over the 9 9 class in foetal cattle 

 twins of the sizes dealt with in this study appears to be real, though it must be 

 admitted that the numbers are too small to make this quite certain. Cole's data 

 on the other hand indicate a great preponderance of the 9 9 class over the d" cf 

 class in cattle twins after birth. It may be t^at abortion, which is so frequent in 

 cattle, is even more adverse to the males in the case of twins than in single births; 

 it is conceivable that the difference is largely a question of viability, but other 

 explanations are possible. 



