SPONGES 31 



great freedom for hours at a time. It must, however, be 

 confessed that not only carmine but even milk is an un- 

 natural substance for a sponge, and as Stylotella lives in 

 water that ordinarily contains much fine suspended ma- 

 terial, it was found necessary only to watch this material 

 to gain all the information that was needed as to the 

 direction or strength of the currents at the pores. 



In testing the pores, a finger of sponge was pinned 

 under the microscope in a small glass aquarium so ar- 

 ranged that a continuous current of seawater could be 

 kept running through it, and by watching the suspended 

 particles along the sides of such a preparation under a 

 magnification of about ninety diameters, it was compara- 

 tively easy to ascertain whether the pore currents were 

 running or not. As a rule the objective of the microscope 

 was necessarily plunged under the surface of the sea- 

 water. In making observations it was, however, neces- 

 sary for the time being to stop the current of seawater 

 that was running through the small reservoir in which 

 the sponge was, otherwise the movement of the suspended 

 particles over the surface of the sponge was so rapid that 

 it was impossible to tell whether they entered a pore or 

 simply glided past it. When this current was shut off, 

 the osculum often closed and under such circumstances, 

 as might have been expected, the pore currents ceased. 

 To be certain that the cessation of these currents was due 

 to the closure of the outlet, the tip of the sponge finger 

 including the closed osculum was cut off with the result 

 that the pore currents almost immediately began again. 

 Moreover, when the cut oscular end of a finger on 

 which pore currents could be easily seen was ligated, 

 these currents ceased at once and on the removal of the 



