54 CARL GOTTFRIED HARTMAN 



At ENT^ an entodermal mother cell has apparently just divided. 

 If we conceive cell ENT^ of figure 28 as dividing across its long 

 axis (that is obliquely to the surface of the blastocyst) , we should 

 have a condition exactly like cell ENT^, figure 29. At M figures 

 29 and 30, a large cell is in mitosis. Its staining qualities, 

 however, do not as yet indicate its entodermal nature. 



Another large cell is in mitosis in a section of No. 40 (2), figure 

 31. The spindle of this cell {ENT-) is oblique to the surface of 

 the blastocyst. At other points (0) there are elongated cells 

 and nuclei with their long axes oblique to the surface. The 

 cell figured at ENT^ is a just divided primitive entoderm cell; 

 and others are shown at ENT. 



A section through the embryonic area of No. 40 (4), illustrated 

 in figure 32, shows at ENT^ a large darkly-staining cell, which 

 one might interpret as an entodermal mother cell that has left 

 its position in the wall of the blastocyst and has migrated to 

 the inner surface. The section also shows several primitive 

 entodermal cells, clearly darker staining than the overlying cells. 

 Blastocyst No. 40 (1) contains several interesting cases of primi- 

 tive entoderm cells (figs. 33 and 34) which give every indication 

 of a tendency to migrate from the original position within the 

 wall, so as to underlie the superficial cells. The cell marked 

 EN'T^, figure 34, is an especially striking case in point. Yolk 

 granules (F, figs. 29, 32 and 33) are of frequent occurrence in 

 these blastocysts, chiefly in the formative region, where, indeed, 

 the only cells thick enough to hold a yolk granule are situated. 



A blastocyst containing a large retarded blastomere is shown 

 in figures 37 and 38. The cell is situated in the blastocyst wall 

 within the formative region, which is rather limited in super- 

 ficial extent. The large cell is almost covered with other cells 

 proliferating from it. The presence of large nuclei in the forma- 

 tive region of other blastomeres indicates that retardation in 

 division of cells is not uncommon. 



The cells of several of the blastocysts just mentioned, show 

 a marked tendency toward rapid multiplication in the formative 

 region, so that this area becomes densely studded with nuclei 



