SPONGES 



41 



small ring of cotton-wool was inserted 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 the finger carrying the osculum was in a strong 

 current of seawater. This form of experiment was re- 

 peated with only the distal fourth of the finger protected 

 from the current, and again the osculum closed in seven 

 minutes. Thus it is only neces- 

 sary 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. 



These experiments were next 

 reversed and attempts were made 

 to ascertain how much of the dis- 

 tal 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 covered the finger all but the tip 

 (Fig. 10). The space between the oscular tip and the 

 tube was filled with cotton-wool and the whole allowed to 

 stand in quiet seawater. After the osculum had been 

 closed for about a quarter of an hour, a gentle current 

 was started across the end of the tube so that it impinged 

 on only the oscular membrane. In three minutes the oscu- 

 lum showed signs of opening and in eight minutes it was 

 fully open. This form of experiment was many times 

 repeated with essentially similar results. The closing of 



Fio. 10. A finger of Stylotella 

 protected from a gentle current of 

 seawater by having apiece of brass- 

 tubing lowered over it and the in- 

 terspace between it and the tubing 

 filled with cotton-wool. The cur- 

 rent impinges only on the tip of 

 the finger, whose osculum never- 

 theless has opened and emits a 

 current of water, as indicated by 

 the arrow. 



