1 62 GEORGE T. MCNAIR. 



If the stimulus was a little stronger, an immediate contraction 

 was followed by a slower general contraction, both lengthwise 

 and in circumference, which would continue for about fifteen 

 minutes, Fig. 4, A and B. The chimney would then begin|to 

 expand and within thirty-five minutes would be almost as large 

 as before. On one occasion the sphincter at the base contracted 

 more quickly than the others, resulting in the form of chimney 

 shown in Fig. 4, C. 



Fig. 4. The arrows indicate the points on each side of the base of the chimney- 

 where the electrodes were applied. 



Stimulation on the Flesh. 



On several sponges the electrodes were applied immediately 

 behind the osculum at distances of from 4 mm. to 2 mm. from it, 

 and the flesh stimulated for periods varying from fifteen to sixty 

 seconds. No effects could be seen on the chimneys. 



There was, however, some indication of an excitation of the 

 choanocytes. The currents were stronger and more rapid for 

 from ten to fifteen minutes after the stimulation. Although 

 this was taken as an indication of greater activity on the part 

 of the flagellate cells, it is possible that the stimulation caused 

 the ostia to dilate or open wider and in this way allow a larger 

 volume of water to pass into the sponge body. It does not 

 seem, however, that this would account for the increased rapidity 

 with which the currents poured out of the oscula. 



There was a noticeable difference in the responses of the 

 oscula to Faradic stimulation depending on the strength of the 

 electrical current used. From a weak stimulus, 1 a very gradual 

 contraction was followed by a more rapid relaxation, while, if 



1 By a weak stimulus is meant one which could barely be detected when the 

 electrodes were applied to the tongue, while by a mild stimulus is meant one that 

 could be felt when the electrodes were applied to the lips. 



