310 
tion of epithelia and endothelia, and shows the fallacy of 
certain objections which have been made to this distinction, 
viz. the supposed occurrence of ciliated epithelium upon 
serous surfaces. Waldeyer had already shown that the 
presence of cilia on the peritoneum is dependent upon the 
peculiar connection of the female sexual apparatus with this 
cavity ; but several observers had thought they had detected 
cilia on the pericardium of the frog. Rollet shows that this 
is an error, part of the peritoneum having been removed with 
the pericardium. 
