204 JOHN LEWIS BREMER 



are apparently of greater extent in animals whose embryos are 

 provided with large Wolffian bodies. 



In the placentae of those animals with a continuous embryonic 

 urinary excretion, similar plates are not found, whether the 

 placentae be of the apposed or conjoined type. 



From these facts it appears that embryonic and fetal urinary 

 excretion takes place wholly through the placenta in the rat, at 

 first through the Wolffian body and later through the placenta 

 in the rabbit, guinea pig, and man, but never through the pla- 

 centa in the pig, sheep, or cat. A knowledge of these differences 

 should lead to more intelligent experiment on the permeability 

 of the placenta. 



