938 CHARLES ZELENY 
this branchia drops off to make place for the rudimentary oper- 
culum developing in its place (fig. 7, B, C). A branchia with a 
small knob-like rudimentary operculum at its end is thus formed. 
This condition is never found in normal development in this 
species but is a normal feature of the adults of the genus Apomatus 
which have also functional opercula with stalks bearing branchial 
filaments (fie. 6:4, B,C 1D): 
B 
q E 
), 
Fig. 7 A, regenerated functional operculum of Serpula type. Individual A 
(no. 2778), on August 3rd. B, branchia next to the dorsal one of right side as modi- 
fied, following operation on the corresponding branchia of the left side. Indi- 
vidual A, (no. 2778) July 31. C, enlarged tip of B. D, rudimentary operculum on 
left side of individual A as developed after the functional operculum of the Serpula 
type had dropped off, August 14. E, functional operculum of Hydroides type as 
developed on the right side of individual A after the functional operculum of the 
Serpula type on the left side had dropped off, August 14. 
G 
It might have been expected that the removal of the functional 
cup would accelerate the breaking off of the corresponding 
branchia of the other side of the body and be followed by the 
development of a normal rudimentary operculum. As a matter 
of fact, the acceleration of opercular development is found, but 
in a way entirely different from the normal. <A group of cells at 
