444 



G. H. PARKER 



jured in detaching the sponge from its natural base or, if it had 

 been necessary to break open the canal system anywhere, such 

 breaks were closed by ligatures of soft string. The tube with the 

 sponge attached was then held rigidly in place in the bucket of 

 water and, after five minutes or so, the height of the water in the 

 tube over that in the bucket was measured by means of a milli- 

 meter rule attached to the side of the tube. Without disturbing 

 the tube and its attached measure, the canal system of the sponge 

 was then cut open so that the water in this system was in free 

 communication with that in the bucket. The water in the tube 

 immediately fell and, after it had come to a constant level, 



TABLE 1 



Showing pressures in millimeters of seawater exhibited by the currents of 

 seven species of sponges from the Bermuda Islands 



NAME OP SPONGE 



HEIGHT OP COLUMN OF SEAWATER IN MILLI- 

 METERS FOR FIVE DETERMINATIONS 



AVERAGE 

 HEIGHT 



Tethya sp. Close to T. seychellen- 

 sis (E. P. Wright) 



Spirastrella sp. Close to S. vaga- 

 bunda, var. tubulodigitata 

 Dendy 



Pachychalina sp 



Spinosella sororia (Duch. et Mich) 



Tedania sp 



Stelospongia sp 



Hircinia variabilis F. E. Schulze. . 



2.5 



2.0 



2.5 



2.0 2.0 



2.2 



a reading of its height was again taken. The difference between 

 this reading and that made before the sponge was cut open was 

 assumed to be a measure of the pressure of the water current 

 produced by the sponge. 



Determinations of the current pressures by the method just 

 described were made in seven species of sponges, and the details of 

 of these measurments are given in table 1. At least five deter- 

 minations were made for each species. I am under obligations to 

 mj' friend, Prof. H. V. Wilson for the identification of the sponges 

 upon which these determinations were made. 



The surprising feature of the determinations in the table is that 

 they all indicate a very low current pressure, lower even than that 



