SPONGES 



45 



tella can be easily tested by tying into its osculum a glass 

 tube of appropriate caliber and by allowing the sponge to 

 work till the column of water in the tube conies to a con- 

 stant level (Fig. 11). By attaching a millimeter scale to 

 the tube this level can then be read, after which the sponge, 

 without disturbance to the apparatus, can be cut off from 

 the tube and the level to which the water in it drops can 

 again be read. The difference between these two readings 

 gives the water pressure generated by the sponge. In 

 Stylotella this proved to be between 3.5 and 4.0 milli- 

 meters. The current produced by Stylotella, then, has a 

 maximum pressure equivalent to a column of water 3.5 to 

 4.0 millimeters in height (Parker, 1910 a). 



Determinations of the current strength on seven spe- 

 cies of Bermuda sponges gave somewhat lower results as 

 shown in Table 2. In these sponges the average pressures 



TABLE 2 



CURRENT PRESSURE IN MILLIMETERS OF SEAWATER AS EXHIBITED BY 

 SEVEN SPECIES OF SPONGES FROM THE BERMUDA ISLANDS 



of the currents varied from 1.3 to 2.9 millimeters of water. 

 It is therefore clear that the pressure of the currents 

 produced in sponges is very inconsiderable. 



The volume of these currents, however, is relatively 

 great and has been determined roughly for Spinosella 

 by the following method. A glass tube of known caliber 



