PLATE X 



Figs. 1-6. Living Physalia rolling in a laboratory tank at Arrecife. 

 Figs. 2, 3 and 5 show phases of the righting motion. The aboral 

 end is raised as in figs. 2 and 3, and after twisting movements falls 

 over as in figs. 4 and 6. The gas-gland can be seen in figs. 1 and 3. 



Fig. 7. Air-sac of Physalia dissected out and fixed in a state of artificial 

 compression (tied off near pore) to show partially inflated dorsal 

 processes, and the disk-shaped gas-gland, x 1-25. 



