THE FCETAL MEMBRANES OF MAN. 261 



The connective substance of the chorionic villi is gelatinous tissue 

 with stellate and spindle-shaped cells in the finer branches ; in the 

 larger stems it takes on a more fibril lar condition. 



The views of investigators are still at variance upon the important 

 point whether the epithelium of the membrana chorii and the villi is 

 of frptal or maternal origin. KOLLIKER, LANGHANS, LEOPOLD, and 

 others derive it from the cells of the serosa, whereas ERCOLANI and 

 TURNER, whom BALFOUR has followed in his text-book, state more 

 or less explicitly that, although originally the cells of the serosa 

 cover the villi as an epithelium, during the mutual intergrowth of 

 the placenta fetalis and the placenta uterina they perish, and are 

 replaced by proliferating cells of the decidua serotina. 



The recent investigations of KASTSCHENKO and SEDGWICK MINOT, 

 as well as the observations of WALDEYER, KUPFFER, GRAF SPEE, 

 and KEIBEL, afford much enlightenment on this controversial 

 subject. 



KASTSCHENKO, who has most carefully investigated the epithelium 

 of the chorion frondosum in the different months of pregnancy, 

 and with whom recently S. MINOT essentially agrees, can readily 

 distinguish two layers : (1) a cell-layer (LANGHANS), which lies 

 immediately upon the gelatinous substance of the villi and the 

 connective-tissue membrana chorii, and in which the limits of some 

 of the cell-territories may be made out, and (2) a multinuclear 

 protoplasmic layer, in which separate cells cannot be demonstrated 

 in any manner. These layers are rather sharply contrasted from 

 each other. 



The double-layered chorionic epithelium is already distinctly 

 present in eggs four weeks old, as is confirmed by KUPFFER, GRAF 

 SPEE, and KEIBEL. The deeper layer consists of a single sheet of 

 well-marked cubical cells ; the outer layer discloses at the free surface 

 a striated border, the significance of which is obscure. 



In the following months the chorionic epithelium undergoes note- 

 worthy alterations. The deeper layer becomes thickened in many 

 places into special cell-patches, in which the elements are much super- 

 posed. The outer, protoplasmic layer changes still more ; it is 

 converted into a hyaline, peculiarly lustrous substance, which is 

 traversed by numerous fissures and spaces, and has therefore received 

 from LANGHANS the name " canalised fibrin." 



There is one conclusion that in my opinion results from these inves- 

 tigations : the view of TURNER, according to which the chorionic 

 epithelium is replaced in the course of pregnancy by uterine 



