126 WINIFRED HUGHES. 



Case No. 4. (Figs, n and 12.) This case presents altogether 

 a different condition from the three previous. A free-martin is 

 a zygotic female co-twin to a male. The twins in this case were 

 two males and measured 6.3 cm. and 7.8 cm. respectively. 

 Their position and orientation in the chorionic vesicle was 

 identical with that of cases Nos. i and 2. The vascular anasto- 

 mosis was stronger than in any other case and was doubtlessly 

 responsible for the difference in rate of growth of the two embryos. 

 Consequent upon an excess of the blood supply being received 

 by one twin, the less fortunate individual was deprived of the 

 full amount necessary for complete growth and normal de- 

 velopment. 



The external genitalia of both individuals was typically male 

 in structure. The scrotal sacs, which were plainly marked in 

 the larger male, however, were indiscernible in the smaller. 



Examination of the internal genital systems, showed the larger 

 individual to be quite normal. The testes, measuring 4.4 mm. 

 by 2.2 mm. had not commenced their descent. The mesonephroi 

 were large and without any signs of shrinkage. Fig. 9, repre- 

 senting a section through the urogenital folds immediately 

 posterior to their fusion, shows the large size of the Wolffian 

 ducts. The Miillerian ducts persist in this region, but farther 

 anteriorly become intermittent. 



The smaller individual presented the condition illustrated in 

 Fig. 12. The testes measured 3.9 mm. in length and 1.2 mm. in 

 tvidth. Descent was in progress, the left having out-distanced 

 the right by more than its own length. Degeneration of the 

 mesonephroi which occurs normally in pigs of 10 cm. or more, is 

 here precocious and irregular. All that is left of the left meso- 

 nephros is a narrow ridge of tissue accompanying the genital 

 ducts. The right has retained its normal size at its anterior 

 end and is extremely irregular in its posterior region. 



On section, the testes proved to be normal in structure. 

 Compared with those of the co-twin, they were more primitive 

 however, being only one half the diameter, and possessing a 

 fewer number of tubules. The tubules contained fewer sex-cells, 

 and a great abundance of inter-tubular material was present. 



Fig. 10, representing a section through the genital ducts at a 



