268 MALL. [Vou. XIX. 
they are invaded at numerous points by the syncytium, which 
forms in them small vesicles, lined with two layers of cells, 
and often filled with dense masses of small round cells. These 
vesicles are very numerous and usually communicate with the 
Fic. 276c.—Section of the embryo. 8% times. 
surface of the villi by means of bands of epithelial cells. The 
walls of the chorion are in apposition to those of the amnion, 
but they are not invaded by syncytium. 
The changes within the embryo are equally remarkable. 
The spinal cord is dilated and dissociated; the medulla is 
