Embryonic Development in Man. 381 



and dropped-off degenerated decidual cells. In section 11 the canal 

 or hole has no covering towards the uterine cavity, but the mass of 

 blood and degenerated, chaotically distributed, decidual cells reaches 

 to the very surface. 



It is clear that this canal, which is more or less circular in 

 outline, with diameters varying from 1.5 to 1.0 mm., indicates the 

 route over which the ovum traveled to the place where it was 

 found in the decidua. It is probable that the ovum after having 

 been fertilized in the tube was brought to a spot indicated by the 

 surface opening in section 11, or thereabouts. The ovum when 

 less than one millimeter in diameter (this measurement, including, 

 of course, the chorionic cavity and the whole then existing tro- 

 phoblast) began to make its way into the decidua. It did, however, 

 not eat its way deeply in at all, but traveled under the surface 

 almost parallel to it, being separated from the uterine cavity only 

 by a very thin strip of decidual tissue, in some places so thin that 

 it became slightly defective, or at least apparently so. After the 

 ovum had traveled through the canal described, of which there are 

 about 200 to 250 micra in lengih left, it must have become sta- 

 tionary and must have begun to exj)and inwardly, towards the 

 muscularis, and also laterally. It is clear that the ovum as found 

 in situ in the decidua is much too large to have traveled through 

 the canal, and it must have been much smaller, probably consider- 

 ably smaller than one millimeter, at the time when this migration 

 took place. 



The canalj as stated, was found moderately well filled with blood 

 corpuscles and degenerated decidual cells. We have, therefore, in 

 our case, unlike Peters, who had in his specimen a mushroom coagu- 

 lum, a still patent, though partly filled, small canal, running almost 

 parallel to the uterine surface, through which the ovum by its own 

 inherent destructive tendencies made its way to the place of final 

 implantation. While the outer end of the canal described com- 

 municates with the surface and is practically open towards it, ex- 

 cept as to the presence of maternal blood and degenerated decidual 

 cells, the inner end is closed by the trophoblast of the ovum. On 

 the opposite point of the ovum, which is found in section 264, where 



