42 THE ELEMENTARY NERVOUS SYSTEM 



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

 water are both very local reactions and cannot be induced 

 from points half a centimeter distant on the finger. 



If the oscula of Stylotella close simply because the 

 water in contact with them ceases to move and not in con- 

 sequence of the accumulation of waste 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 of air is lowered over a finger 

 whose osculum is open till the oscular membrane just 

 comes in contact with 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 con- 

 dition of quiescence into which the tip of the finger passes 

 in going from the water into the gas. 



If a finger of Stylotella is cut off about a centimeter 

 from the osculum, that aperture even in a current of sea- 

 water is likely to close within a short time and to remain 

 closed for an hour or more. If the finger is cut off at two 

 centimeters from the osculum, there is less likelihood of 

 the closure of the osculum than when the finger is cut at 

 one centimeter. If a pin is stuck into a finger at one and 

 a half centimeters from the osculum, this opening will 

 close in about ten minutes. Thus injury to an adjacent 

 part will bring about a closure of the osculum. The nature 

 of the stimulus produced by injuring the flesh of a sponge 

 seems to be rather mechanical than otherwise. Such an 

 injury besides disrupting the tissues mechanically does 

 little more than liberate their juices. These juices, how- 

 ever, when collected and discharged on a normal sponge 

 with open oscula do not cause the oscula to close. Hence 



