876 THE AMERICAN NATURALIST. 
Clausilia, have respectively a normal and reversed cleavage. 
So far as the facts are known at present, they seem to jus- 
tify the view that the reversed asymmetry of the sinistral 
gasteropods owes its origin to a reversal of cleavage of 
the egg. 
UNIVERSITY OF MICHIGAN, 
October 13, 1899. 
