CONTROL OF .ASYMMETRY IN HYDROIDES 933 
Ls 
Fig. 2 Young Hydroides dianthus with six branchiae (individual C, no. 2780). 
The most dorsal pair has not yet developed its pinnules. The levels of the cuts 
made in the operation are indicated by C. 
Fig. 3 Hydroides dianthus, age 34 days; stage with four pairs of branchiae. 
The next to the dorsal one on each side is shown in full. The left one shows the 
beginning of the knob of the functional operculum. The right one drops off later 
and the first rudimentary operculum is developed from its stump. 
