MOTOR REACTIONS OF THE FRESH-WATER SPONGE. 



I63 



the stimulus was mild, there would be an immediate contraction 

 followed by a slower more general contraction. In this case the 

 chimney would remain contracted for a few minutes and then 

 expand much more slowly than it had contracted. In the second 

 instance, all of the contractile cells probably were directly 

 stimulated by the electrical current, while in the first case it is 

 probable that only those where the electrodes were applied were 

 directly stimulated, the gradual contraction being the result of 

 transmission of the stimulus from one cell to the next. 



In one instance, following a very weak stimulation for thirty 

 seconds, it was possible to keep an accurate measurement of the 

 time required for contraction and relaxation of the sphincter at 

 the mouth of the osculum. No check was made on the general 

 contraction or relaxation of the chimney. That the contraction 

 was slower than the relaxation is shown by the following graph. 

 The temperature of the water was about 27 C. 



Min. 5 10 15 20 25 30 35 40 45 50 55 60 65 70 



Fig. 5. Graph showing the rate of contraction and of relaxation of the sphincter 

 at the mouth of an osculum following a weak Faradic stimulation. The abscissa 

 represents the intervals of time in minutes and the ordinate the diameters of the 

 opening in millimeters. 



Transmission of Stimuli. 



It has already been pointed out that, apparently, very little 

 transmission from one part of the body to another resulted from 

 the application of the various types of stimuli used in these 

 experiments. To determine if there was any transmission at all, 



