CELLS LINING THE PERITONEAL CAVITY 419 
eylindrical layer of cells which lines the peritoneal cavity during 
its formation from the coelomic layers. Later, the special 
characteristics of the germinal epithelium are developed in 
connection with their further differentiation into sexual elements. 
Furthermore, he found that the flat serosal cells of other areas 
in the peritoneal cavity of frogs may be transformed into typical 
germinal epithelium when sexual maturity is reached. 
MacLeod (80) suggests that the peritoneal epithelium also 
undergoes modifications in other regions, e.g., spleenand pancreas, 
and Kolossow (’93), in his careful studies of the normal peritoneal 
epithelium in both mammals and amphibia, comes to the con- 
clusion that the germinal epithelium of the ovary is a part of 
the true layer of peritoneal lining cells, which, owing to specific 
stimuli, has undergone a certain amount of differentiation. He 
also found certain differences in the cells covering the spleen in 
mammals and in those covering the stomach of amphibia. 
Coert (98) believes that the germinal epithelium is formed 
from the general coelomic epithelium and denies its specificity 
in Waldeyer’s sense, but agrees with him that the germinal 
epithelium gives rise to primordial germ cells. 
Van Beneden (’80), Allen (’04), Sainmont (’06), working with 
the cat, Firket (14), (20 a), using the chick, and others have 
come to the conclusion that the germinal epithelium of the ovary 
is a part of the peritoneal mesothelium which has become 
cylindrical. Even Waldeyer in his more recent work has modified 
his earlier opinions indorsing the conclusions of Coert. In 
general all modern work has tended to establish the genetic 
continuity of the general peritoneal serosa and the germinal 
epithelium; whatever the factors may be that determine the 
specific changes which have been found in the cellular layers, 
particularly of those over the ovaries, but also to some extent 
of those covering the spleen, stomach, etc., they must be asso- 
ciated with some stimulus coming from the structures over which 
the changes take place. 
The results of the vital staining of the germinal epithelium 
and the cells of the general peritoneal lining indicate a certain 
similarity in the reactions of these two groups of cells. There 
