44 



Charles Zeleny. 



the older branches of II. L-II — -i has two branchlets ( =. pin- 

 nules) and R-II — I has one branchlet. Branchia II on each side 

 now shows the beginning of the sixth branchlet or pinnule. 

 Branchia III also has not increased much in size. 



In Fig. 12 (23 days old) Branch II — i with its six pinnules has 

 very evidently taken its place as a prominent part of the branchial 



Fig. 12. 



Hydroides dianthus. Age, 23 days (X75). The first secondary branch of Branch II has assumed 

 the character of an independent main branch with branchlets of its own. The original third pair of 

 branches is not shown. 



apparatus. Branchia II has now added its eighth pinnule. 

 Branchiae I and III are still unbranched and have increased com- 

 paratively little in size. 



In Fig. 13 (23 days old), in which only the right side is repre- 

 sented as both sides are essentially similar, Branchia I for the first 

 time shows a trace of branching, seven little branchlets (pinnules) 

 appearing simultaneously. Branchia II has added one new 

 branchlet making nine in all counting Branchia II — i as the first 



