14 G. H. Parker 



covered the finger all but the tip. 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 osculum showed signs of opening and in eight 

 minutes it was fully open. This form of experiment was many 

 times repeated with essentially similar results. It is therefore 

 necessary for the current to impinge on only the oscular tip of the 

 finger in order that the osculum shall open. The closing of the 

 osculum in quiet water and its opening in a current of water are 

 then both very local reactions and cannot be induced from points 

 on the finger a quarter of its length (about half a centimeter) from 

 the osculum. 



If the oscula Stylotella close simply because the water in their 

 immediate vicinity ceases to move and not in consequence of the 

 acculumation of waste products or lack of oxygen, they probably 

 close in the air on a falling tide because of the same mechanical 

 conditions. If in the laboratory an inverted test-tube full ot air is 

 lowered over a finger whose osculum is open till the oscular mem- 

 brane justcomes in contactwith the air, the osculum closes in about 

 three minutes. The same result can be obtained when the test- 

 tube contains washed hydrogen in place of air. Hence this 

 reaction is not due to the oxygen of the air, but is very probably 

 induced by a purely mechanical condition of quiescence into which 

 the tip of the sponge finger passes in going from the water into the 



gas. 



If an osculum opens to the mechanical stimulation of a current 

 and closes in its absence, it is reasonable to suppose that it might 

 respond to the stimulation produced by touching it with a bristle 

 or stroking it with a fine brush, but my attempts in these directions 

 were not conclusive. Touching or stroking an oscular membrane 

 inside or outside when the osculum was open and in a current of 

 seawater never resulted, as might have been expected, in a con- 

 traction of the osculum. Similar attempts on the outside of a 

 closed osculum in quiet seawater occasionally resulted in a partial 

 opening of the aperture, but these occurrences were so irregular 



