SEX-INTERGRADES IN FCETAL PIGS. 125 



Case No. 2. This case is practically a repetition of the one 

 just described. The twins measured 45 mm. and were hetero- 

 sexual. Their position in the chorionic vesicle and the orientation 

 of their membranes was similar to case No. I. Anastomoses of 

 veins occurred in places marked in Fig. 4. The same abnormality 

 of the female sex-equipment was present here also, but this 

 being a slightly younger stage, the medullary cords were more 

 conspicuous, and still retained their cord-like structure. The 

 cortical zone of secondary cords was again represented by a few 

 clumps of degenerating cells in the tunica albuginea. 



Case No. j. (Fig. 2.) This case differed from the previous in 

 that the monochorionic condition had arisen from end-to-end 

 fusion of blastocysts. This was evident both from the double 

 length of the chorionic vesicle, and from the orientation of the 

 embryos and their membranes. The zone at which fusion had 

 occurred was indicated externally by a mere thinning of the 

 placenta which stretched uninterruptedly across this zone, with- 

 out leaving any signs of imperfect fusion in the form of persistent 

 necrotic areas. The blood vessels of the two circulations here 

 came into contact and inter-communicated by means of distinct 

 venous anastomoses. 



The foetuses measured 9 cm. Modifications of the female 

 sex-equipment have resulted in small testis-like gonads com- 

 pletely devoid of any trace of secondary sex cords (Fig. 8). In 

 no place is the germinal epithelium more than one cell in thick- 

 ness, indicating that secondary sex-cords, if present earlier, have 

 by now been completely re-absorbed. The underlying tunica 

 albuginea is typically male in structure, even to the extent of 

 penetration of blood vessels. The medullary region is con- 

 spicuous and contains numerous sex cells arranged in clumps. 

 These are being surrounded by connective tissue growing in 

 from the tunica, and have thereby the appearance of early 

 seminiferous tubules. 



The Wolffian ducts were large throughout their entire course, 

 not showing the normal degeneration at their anterior portions, 

 and the Miillerian ducts had followed the male course of growth 

 in becoming discontinuous in the region immediately posterior 

 to the gonads. 



