Reactions of Sponges 13 



open when the tube was lowered over the finger, it closed in seven 

 minutes after the tube was in position and remained so for a quar- 

 ter of an hour. I now inserted a small tube into the upper end of 

 the large tube and ran a gentle current of seawater down into the 

 end of the large tube where the finger was situated. Thus the 

 sponge was again in a current of seawater and in fourteen minutes 

 its osculum was fully open. On cutting off this current, the oscu- 

 lum closed in six minutes. From these experiments it is quite evi- 

 dent that when no current of seawater impinges on a finger, its 

 osculum closes and when such currents do strike the finger the 

 osculum opens. It was noteworthy that during the time of these 

 experiments the oscula in the immediate neighborhood of the one 

 tested showed no changes in reference to those observed in the 

 individual within the tube, but they remained for the most part 

 persistently open in the general current of seawater. 



The next question that naturally suggested itself was how much 

 of a finger must be exposed to a current of seawater to induce the 

 opening of its osculum. To test this, I placed the glass tube over 

 the distal half of a finger leaving the proximal half exposed to the 

 general current. I found, however, that the current eddied up into 

 the tube and thus impinged on a part of the sponge supposed to be 

 protected from it. To check this I inserted a small ring of cotton- 

 wool between the free end of the tube and the sponge. Under 

 these conditions the osculum closed in eight minutes even though 

 the lower half of its finger was in a strong current of seawater. 

 This form of experiment was repeated with onlv' the distal fourth 

 of the finger protected from the current, and again the osculum 

 closed in seven minutes. Thus it is only necessary to have 

 quiet water around the outermost fourth of a finger to cause its 

 osculum to close, and a strong current on the proximal three- 

 fourths of the finger will not induce the osculum to open. 



I next reversed these experiments and attempted to ascertain 

 how much of the distal tip of a finger must be exposed to a current 

 to induce the opening of its osculum. In making these trials, a 

 piece of light-weight brass-tubing was cut to such a length that 

 when it was slipped down over a vertical finger of the sponge, it 



