398 FRANK R. LILLIE 



apart when removed; injection of the chorion of the male showed 

 its circulation to be entirely closed. Dissection of the female 

 showed its reproductive system to be perfectly normal (fig. 6); 

 sections of the gonad showed it to be an ovary (Chapin, '17); 

 each maternal ovary had a corpus luteum in it. Even though 

 this case stands alone, it is obvious that it fulfills all the con- 

 ditions of a radical experiment; so that we can say that foetal 

 vascular anastomosis of two-sexed twins involves the sterile 

 condition of the female, and absence of such anastomosis its 

 fertile condition. 



The sheep and other normally uniparous ruminants should 

 furnish another test of the theory; for though twin births are 

 fairly common in sheep the female of two-sexed pairs is usually 

 norrhal. This is a matter of common experience among breeders, 

 and is strikingly demonstrated by Prof. Alexander Graham Bell's 

 well-known experiments (Bell '12) on the production of a multi- 

 nippled race of sheep ; 36 per cent of the lambs born on Professor 

 Bell's farm were twins; and in 1912, 60 per cent of the lambs 

 born from three year old ewes were twins; the records show that 

 the twin ewes are used commonly for breeding purpose, ^vhich 

 would not be the case if any considerable percentage were sterile. 

 The fact that there is no reference in this very careful series of 

 experiments to sterility of ewes from two-sexed twins would also 

 show that such a phenomenon must be at least very uncommon. 

 On the other hand Bateson states that it sometimes occurs 

 among sheep; though, on what authority, I do not know. 



In response to a letter of inquiry Wm. John G. Davidson .who 

 has had charge of the breeding operations at Dr. Bell's estate 

 for a great nlany years writes: 



I may saj'' that in all my experience in sheep breeding I have yet to 

 find a case where lambs born twin to males have turned out sterile. 

 In fact when lambs are born twin male and female if they have the 

 desired qualifications required in the flock both lambs would be retained 

 in the flock and I have not had the slightest trouble with either male 

 or female being unfruitful. I know there is nothing in the free-martin 

 theory in sheep breeding. 



It was therefore very interesting to examine twin pregnancies 

 of sheep with reference to the relations of their membranes. I 



