STUDIES IN MAMMALIAN EMBRYOLOGY. 355 
shield the epiblast of the blastocyst is split up into two layers. 
The upper layer consists of flattened cells and remains adjacent 
to the uterine epithelium. From this layer a stratified layer 
of high cylinder-epithelium is separated as a second layer of 
epiblast. We are justified in regarding the more superficial 
layer of flattened cells as homologous to Rauber’s ‘ Deckschicht’ 
of other Mammalia, the layer of high cylinder-cells as the 
definite epiblast of the embryo.” 
Now, it will be clear that the process here described by 
Keibel is identical with the one described by me some months 
earlier at the Wiirzburg Congress, where I said (1. ¢., p. 511), 
** A circumscribed region of the primitive trophoblast splits off 
(as in the mole) from the rest and is bent inwards, whereas it 
remains connected with the remainder of the trophoblast along 
the whole circumference. It becomes the epiblast of the ger- 
minal area. . . . As the blastocyst increases in size the 
trophoblast thins out and becomes the villiferous outer wall of 
the blastocyst.” It is the same process that was fully entered 
into above (p. 288) and that is figured on Pl. XVI, figs. 14: to 
20, 15 a, 17 a, and 20 a. A comparison of Keibel’s descrip- 
tion here cited with figs. 7 @ and 10a will convince the most 
reluctant. 
Ad 2. It follows from the foregoing argumentation that 
the process there referred to and described both by myself and 
subsequently by Keibel may safely be admitted to exist in the 
hedgehog, and can be directly compared to what Heape ob- 
served in the mole. But as this is the process of formation of 
the epiblast of the embryonic area out of the epiblastic wall of 
the blastocyst, it is not in any sense comparable to van Bene- 
den’s process of subdivision (also figured by Frommel) of the 
bat’s trophoblast into two layers, which he has termed plas- 
modiblast and cytoblast. This subdivision not taking place 
in the hedgehog it is all the more advisable to retain the 
general name of trophoblast, reserving van Beneden’s terms 
for such cases where the subdivision actually does take place. 
If I may venture to account for the origin of Masius’s mis- 
understanding of Keibel’s description, I would feel inclined to 
