MOTOR REACTIONS OF THE FRESH-WATER SPONGE. 1 57 



Within thirty minutes after taking the sponges out of the swift 

 current the chimney had again extended to about half of its 

 original length. The osculum was slightly contracted. 



The current had caused the sponges to roll and tumble over 

 the bottom of the dish to some extent. To find out if this had 

 been the cause of the shortening of the chimneys, the sponges 

 were placed in watch glasses which, in turn, were placed within 

 the larger dish. When the water was turned on, the force of the 

 current against the curvature of the watch glass held the sponges 

 in place. This time a swift current flowed over the sponges 

 but they did not roll about. Within twenty minutes the chim- 

 neys had flattened out as before. 



The sponges were now placed in a large jar in which a slow 

 current of water was kept going. After being there for a few 

 hours the chimneys were found to be well extended and with 

 strong currents coming out through them. 



Neither the absence of currents nor the presence of strong 

 currents causes the osculum to close although the latter does 

 cause a general shortening of the oscular chimney. In small 

 quantities of water, however, the sponges soon became less 

 active and in time died; the smaller the quantity of water the 

 sooner the changes could be noticed. This effect could not have 

 been due to the absence of the mechanical stimulus of flowing 

 water, because if placed in a large tank of quiet water the sponges 

 will live for a long time. Nor could it have been caused by 

 lack of oxygen, because the dishes which were used were large 

 and shallow so that the water was well exposed to the air. It 

 must have been produced then by self -poisoning from the prod- 

 ucts of metabolism that accumulated ' in the small quantity of 

 water. The greater general vitality of the sponges when placed 

 in slow running water or in large tanks of quiet water is accounted 

 for by the fact that these products were removed as they were 

 thrown off by the sponges or were diffused through the large 

 volume of water. 



These results are entirely different from those obtained by 

 Parker from somewhat similar tests with Stylotella. When he 

 transferred Stylotella from the natural habitat to tanks of quiet 

 sea water, the oscula invariably closed within ten minutes and 



