131 



on the anti-mesometric side, and to the right and left of the 

 embryo, undergoiüg rapid proliferation. Mitoses are freqnently met 

 with (Fig. 17a) and many of the closely packed polyhedral cells 

 contaiu two or three nuclei. 



Between the cells is a fibrillar substance which may be made 

 to stain intensely with nigrosin and other acid stains. 



Tbe cells are smaller as well as less numerous on the rneso- 

 metric side. As a result of this active cell-multiplication the 

 glands are gradually pushed far away from the lumen of the uterus, 

 and are now only to be found immediately underneath the mus- 

 cularis. Their necks, the lumina of which becorue occluded, are con- 

 sequently drawn out into long cylinders of stretched cells, surrounded 

 by one or more layers of flattened subepithelial tissue. (Fig. 1). 



Externally the position of the embryo in the uterus is now 

 marked by a swelling which is most conspicuous on the anti- 

 mesometric side. 



The omphaloidean trophoblast during the Jirst and 

 following period. 



The first period, to which we now pass, is characterized by 

 the definite attachment of the embryo to the walls of the pit in 

 which it lies, and from which the epithelium now wholly dis- 

 appears. In the embryo itself the yolk-sac is completed, the me- 

 soderm laid down and the placental trophoblastic thickening 

 formed at the embryonic (the mesometric) pole of the blastocyst. 

 In the embryonic knob, which is now invaginated into the prox- 

 imal wall of the yolk-sac, a cavity, the amniotic cavity, appears 

 and after being in temporary communication with a transitory 

 cavity (Selenka's 'Falsche Amnion-höhle') in the placental tropho- 

 blast, becomes separated from the latter by the formation of the extra- 

 embryonic ccelom, into which space the allantois grows out as a 

 solid mass to attach itself to the somatopleure. (Figs. 1 — 3, 7 — 9, 

 12, 13 Compare Selenka, Figs. 10, 11, 12, 15, 16, 17, 20, 21, 

 29, 37, 38, 43). 



Many of the cells of the trophoblast, especially in the ompha- 



