SUPPLEMENTARY NOTES ON TWINS IN CATTLE. 6 1 



after birth in free-martins, and I therefore assumed that their 

 appearance in the free-martin was probably belated. A reexam- 

 ination of the material, however, shows that they are always pres- 

 ent in fcetal free-martins in which the lower part of the Wolffian 

 ducts is developed. Fig. 5 from a specimen hitherto not recorded 

 (case No. 94) shows the typical condition in a free-martin with 

 well-developed Wolffian ducts. 



Reexamination of the specimens figured in my 191 7 paper shows 

 similar structures, sometimes more slender, in those represented 

 by Figs. 14, 15, 17, 18, 20, 21, 22, 24, 25, and 27. On the other 

 hand, the specimen shown in Fig. 26 had no Wolffian ducts and 

 no seminal vesicles. The other specimens figured were not avail- 

 able for reexamination. The specimens were drawn correctly, as 

 dissected at the time the drawings were made ; it required further 

 dissection to reveal the seminal vesicles (cf. Fig. 5 of this paper 

 with the figures of the 1917 paper). 



This correction removes the necessity for the special assumption 

 made in the 191 7 paper that these organs develop out of their 

 due time. 



6. The Earliest Stage of the Free-martin. 



The smallest free-martin hitherto described is 7.5 cm. greatest 

 length, case 19 of my 191 7 paper. The gross anatomy was de- 

 scribed and figured by myself, and the histology by Miss Chapin 

 (1917). The normal female characters are highly modified at 

 this stage; the ovary exhibits a serous covering and albuginea 

 similar to that of the male, absence of the ovarian cortex, and 

 presence of the medullary components of the ovary. In the nor- 

 mal ovary of the same stage the cortex is highly developed, though 

 Miss Chapin states that the cords of Pfliiger are not yet separated 

 from the germinal epithelium. The Mullerian ducts of the free- 

 martin have begun to degenerate similar to a normal male of corre- 

 sponding age (Chapin, p. 459). It is, therefore, apparent that the 

 modifications of the free-martin must start at a considerably earlier 

 stage. 



From a study of the chorionic vesicles of normal single preg- 

 nancies I concluded that the opportunity for fusion of embryonic 

 membranes from a two-sided twin pregnancy is present from the 



