940 CHARLES ZELENY 
of serrations (.e., of the Hydroides type). The new operculum 
is about half developed. 
August 14. 
Left side. The functional operculum of the Serpula type has 
dropped off and a rudimentary operculum has developed in its 
place (fig. 7, D). 
Right side. ‘The functional operculum of the Hydroides type 
is fully developed (fig. 7, B). 
Individual B. (No. 2779) 
July 1. Egg fertilized. 
July 28. Condition of opercula as in no. 2778 on July 27. 
Operation. 'The opercular enlargement at the end of the bran- 
chial operculum was removed (fig. 4, level B). 
July 29. ; 
Left side. Removed opercular cup is regenerating (fig. 4, Ba). 
August 3. 
Left side. A functional operculum of the Serpula type is fully 
developed. The respiratory pinnules have already disappeared 
(fie = 5)c 
Right side. The next to the dorsal (second) branchia has 
dropped off and a rudimentary one has developed in its place (fig. 
5). 
August 7. 
Left side. Functional operculum of Serpula type. 
Right side. The rudimentary operculum has developed into a 
half-grown operculum of the Hydroides type. 
August 14. 
Left side. Rudimentary operculum (7, D). 
Right side. Functional operculum of Hydroides type (7, £). 
Individual C. (No. 2780) 
July 1. Eggs fertilized. 
July 28. 
Condition of opercula and branchiae. Three pairs of branchiae 
are present. The most dorsal pair has not yet developed its 
pinnules. There is no sign of opercular enlargement (fig. 2). 
