PLATE I. 



Fig. 1. — Upper end of pneumatocyst, showing "bald-head" with the 

 bases of the frond clusters. 



Fig. 2. — View of kelp bed with bald-heads in foreground. 



Fig. 3. — Upper end of pneumatocyst covered by Lacuna eggs. 



FlG. 4. — Upper end of pneumatocyst, showing tracings made by 

 Lacuna when eating. 



Fig. 5. — Fragments of frond with several snails; badly eaten. 



FlG. 6. — Float, showing appearance at close of experiment. 



Fig. 7. — Colonies of Membraniphora membranacea on a frond. 



