40 THE ELEMENTARY NERVOUS SYSTEM 



of the sponge so that the tube protected the length of the 

 finger from the laterally impinging current but was at 

 no place in contact with the finger (Fig. 9). The water in 

 this tube on examination was found to be for the most 

 part quiet ; its condition, however, did not interfere with 

 the slight currents produced by the sponge itself. Al- 

 though the osculum of the finger 

 under examination was fully 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 quarter of an 

 hour. A small tube was now inserted 

 fV \J "V into the upper end of the large tube 

 fjT~j I I \ surrounding the finger and a gentle 

 current of seawater was run down 



Fio. 9. Fingers of Stylo- . ,. 



tella in a strong current of sea- into the Water SUrrOUndlUg the 

 water. One finger is protected 



from the current by haying a linger. In tourteen minutes the 



glass tube lowered over it and 



t 



closed; the oscula of the other OSCUlum WES again fully Open. Oil 



feT/L^sho^nVy^hra^rows: cutting off the current the osculum 



closed in six minutes. It is note- 

 worthy 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 continuously open in the general cur- 

 rent of seawater. 



The next question that naturally suggested itself was 

 how much of a finger must be exposed to a current of sea- 

 water to induce the opening of its osculum. To test this, 

 ;i iclass tube was made to cover the distal half of a finger, 

 leaving the proximal half exposed to the general current. 

 To check the eddying of the current up into the tube a 



