DEVELOPMENT OF THE PIG DURING FIRST TEN DAYS. 349 



Another specimen (PI. 25, fig. 12, A) shows a large isolated 

 fragment not actually fused nor continuous with the edge of 

 the trophoblast. Fig. 39 represents a section taken through 

 this specimen. At no point is there any complete fusion 

 between the fragment and the underlying epiblast, as in the 

 last case (fig. 36). 



Another specimen has a long fragment, clearly a continua- 

 tion of the trophoblast, running across the surface of the 

 embryonal area (as in the case of figs. 33, 37), but in this 

 instance it ends freely, and at no point is it attached to the 

 embryonal area below. In the same section (fig. 39) a single 

 cell (T.R.) may be seen, which from its appearance, colour, 

 position, and prominence above the others seems undoubtedly 

 to owe its origin to the trophoblast layer. Such cells are not 

 rare but by no means numerous. The number of them com- 

 pared with that of the cells of undoubted inner mass origin is, 

 however, quite insignificant. 



Now it seems to me that such structures as the above- 

 mentioned irregular masses, and the appearances described by 

 Weysse, are to be explained in this way. 



After the trophoblast has ruptured during the tenth day, in 

 the accomplishment of which process I assume that the local 

 tension produced by the growth and lateral expansion of the 

 epiblastic mass plays an important part, the ragged edges of 

 the ruptured trophoblast and the isolated cells of the same 

 layer are by no means forced to die or to degenerate imme- 

 diately. On the contrary, they grow and multiply, and grow 

 into almost any shape, and form balconies, bridges, &c. After 

 some hours they become, for the most part, rubbed off or 

 swept away by the action of the uterine ciliated cells, and by 

 contact with the walls of the uterus. Some few cells which 

 have become more closely attached, like T.R. in fig. 39, or 

 those at the point of fusion {T.R.) in fig. 36, remain for a longer 

 time as part of the embryonal area. Whether, however, any 

 of them become permanently part of it I am quite unable to 

 say. I cannot trace any further than the condition of the 

 single cell {T.R'.) in fig. 38 or 39, 



