MOTOR REACTIONS OF THE FRESH-WATER SPONGE. l6l 



wave of contraction down the entire length of the chimney. 

 This wave traveled down at the rate of about 1.5 mm. in four 

 seconds. A strong stimulus applied to the chimney caused 

 a complete relaxation, as though paralyzed, and from which it 

 did not recover. 



Stimulation at the Sides of the Chimney. 



Choosing chimneys which were long and well extended the 

 electrodes were applied at one side of the chimney, Fig. 3, A. 

 When a weak stimulus was used, the response required about 

 one minute before it appeared. A mild stimulus resulted in an 

 immediate response. First, the chimney would bend toward 

 the electrodes, the bending occurring at the points where the 

 wires touched the chimney, Fig. 3, B. This bending always 

 occurred within thirty seconds from the time the stimulus was 

 started. At the same time, but continuing longer, the entire 

 chimney would shrink slightly. This slow shrinking continued 

 for from one to five minutes. If the wires were applied to the 

 opposite side (Fig. 3, C) while the chimney was still bent as in 

 (B), within one minute the end of the chimney would swing 

 over in that direction, Fig. 3, D. Within thirty minutes the 

 chimneys would straighten and expand to their former size 

 and shape. 



Fig. 3. The arrows indicate the points on the side of the chimney where the 

 electrodes were applied. 



Stimulation at Base of Osculum. 



When a very weak stimulus was given for fifteen seconds with 

 an electrode at each side of the base of the chimney, a very 

 gradual longitudinal shrinking could be observed. The time 

 required for the contraction to travel from the base to the tip 

 was ten seconds, a rate of transmission of 0.17 mm. per second. 



