936 CHARLES ZELENY 
sary to assume further reversal or reversals of position during 
later development and perhaps throughout adult life. 
The original asymmetry is apparently always of the same na- 
ture, 2.e., the functional operculum always develops on the left 
A 
Fig. 6 A, B, C, D, Apomatus ampullifera. Adult. A, dorsal view showing 
functional and rudimentary opercula and branchiae. Pinnules not represented 
(X 5): B, tip of non-operculate branchia (x 17). C, tip of rudimentary operculum 
(X 17): D, tip of functional operculum (X 17): £#, distal portion of functional oper- 
culum of Serpula vermicularis (xX 19). 
side and from a particular branchia. Adult individuals differ 
in character because some have had an odd and some an even 
number of reversals. 
