392 FRANK R. LILLIE 



the investigation began was that the free-martin and its twin 

 were monozygotic, and it was not until after 27 cases had been 

 examined that I was convinced that they were dizygotic. The 

 real explanation of the phenomenon then for the first time be- 

 came evident. No vascular injections were therefore made 

 during the first part of the investigation, and the evidence for 

 vascular anastomosis among these rests upon incidental obser- 

 vations, the significance of which was not realized at the time. 

 Relatively few of the twin ova received thereafter were in a fit 

 state for complete injections. Of the 28 cases involved injections 

 were made only in seven cases; two of which will be described in 

 detail below. But in 21 of the 28 cases vascular anastomosis 

 could be satisfactorily demonstrated either in the uninjected 

 chorions or in injections. Some of the uninjected cases were 

 just as demonstrative as though they had been injected. In 

 four cases of the remaining eight there was no anastomosis; 

 one too young (no. 49) ; the second was a case of normal male 

 twins in which the connection between the two chorions was 

 merely a narrow band-like connection (no. 46) ; the third was a 

 case of male twins \\ith entirely separate chorions (no. 56); 

 the fourth was another case of completely separate chorions (no. 

 40) of the greatest theoretical interest because one foetus was 

 male and the other a normal female. Finally there were three 

 cases wdth inadequate records. Eliminating these three we 

 have 25 cases, in 21 of which, including the three possible twin 

 combinations, vascular anastomosis could be demonstrated and 

 4 in which it was absent (nos. 40, 46, 49, and 56). 



This is not, however, the only evidence that more or less com- 

 plete vascular anastomosis between the pairs is the rule in cattle 

 twins. I can distinctly remember the continuity of the thickened 

 chorionic band that carries the main arteries as the rule in the 

 first 27 cases, and this was recorded in certain cases in my 

 notes. 



There cannot be the least doubt that in bovine twdns fusion 

 of the chorions usually occurs and is followed by anastomosis of 

 the blood vessels of the two sides, and that intermixture of the 

 blood of the two foetuses results. Nor can it be doubted that 



