418 R. S. CUNNINGHAM 
far obtained tends to indicate that the serosal cell is a specific 
cell-type and is not a transformed fibroblast, in the sense of being 
interchangeable morphologically and physiologically. 
The relation which the germinal epithelium bears to the ovary 
and to the cells lining the general peritoneal cavity has been 
extensively studied. In the course of these investigations there 
have developed two principal questions, both of which must be 
considered in the light of the reactions which these groups of 
cells manifest towards vital dyes. In the first place, are the 
germinal epithelial cells closely related to the cells lining the 
general peritoneum, or are these two groups entirely different 
genetically and functionally? In the second place, to what 
extent do the follicular cells, interstitial cells, and definitive 
ova have their origin in these cells which constitute the ovarian 
envelope? 
Waldeyer (’70), after long and careful study of many species, 
decided that the cells of the general peritoneal mesothelium were 
in early stages entirely similar to, and continuous with, the ger- 
minal epithelial cells. But later in the developmental history, 
all of these cells except those over certain specific areas, differing 
in different species, were destroyed or desquamated and their 
place taken by subjacent connective-tissue cells. He found that 
in the amphibia the cells of the general serosa retained their 
primitive characters in wider distribution than in the mammals, 
and so he considered that the peritoneal sac might be thought 
of as fundamentally a reproductive pouch which gradually was 
narrowed until, in mammals, this property was retained only 
by the cells of the ovarian envelope. 
Gatenby’s work (’16) on the frog, in which he found that the 
general peritoneal lining cells could bud off and produce ova, is 
in support of Waldeyer’s idea. But, on the other hand, many 
observers have considered the cells covering the genital ridge as 
being differentiated out of the general coelomic layers. 
Neumann (’75) found that there were interesting interrela- 
tionships between the cells covering the ovary and those lining 
the general peritoneal cavity in the frog. He considered them 
genetically identical, because they both arose from the low 
