446 G, H. PARKER 



still a free flow from it. A cut was made on the side of the sponge 

 at the level of the outer seawater and the sponge was taken to the 

 laboratory. Close measurements showed that the edge of the 

 osculum over which the water lifted by the sponge had been 

 flowing was 4 mm. above that of the sea level, demonstrating that 

 this sponge in the undisturbed condition in which it was found 

 had been overcoming a pressure of 4 mm. of seawater. As the 

 highest pressure that had been obtained from Spirastrella in the 

 laboratory was 2.5 mm., it seems probable that the laboratory 

 determinations for all the species tested are a little below the 

 actual maxima for this form of activity, though, for reasons 

 already given in my former paper on Stylotella, they cannot be 

 much below this maximum. 



From these observations it is clear that the currents produced by 

 sponges consist of relatively large volumes of water flowing at 

 low pressure and that currents of this kind are capable of producing 

 such deformations of the surface of the sea as can be observed 

 above large sponges. It would be interesting to ascertain what 

 proportion of the suspended material in the seawater is screened 

 out as the current passes through the sponge, but no observations 

 on this point were made. 



