MOTOR REACTIONS OF THE FRESH-WATER SPONGE. 1 59 



into the body of the sponge 3 mm. from the base of the chimney 

 without causing any change in the rate of the currents or in the 

 size of the chimney. Another cut right at the base of the chimney 

 caused it to close. It did not reopen for two days. This cut 

 was so near the chimney, however, that the closing was probably 

 due to cutting into the chimney cavity and when this had healed 

 over the chimney again expanded. The result of such injuries 

 differs from the effect of similar ones on Stylotella, where a cut 

 from 3 mm. to 5 mm. from the osculum was found to cause 

 closure within nine minutes. 



Pin Sticking. 



Sticking a needle into the flesh of the sponge at a distance of 

 2 mm. from the osculum caused no noticeable effect on the 

 osculum. The same type of injury 5 mm. from the osculum of 

 Stylotella resulted in the osculum closing within ten minutes and 

 remaining closed for several hours. 



Exposure to the Air. 



A sponge was lifted from the water and held in the air for 

 three minutes. A large chimney was noticeable before, but 

 could not be found after placing the sponge back in the water; 

 neither could it be found at any later time. 



Thermal Responses. 



The average temperature of the water in the tanks in which 

 the sponges were kept was about 27 C. Eight of the sponges 

 which had well developed oscular chimneys and from which 

 strong currents of water were flowing were placed in dishes in a 

 refrigerator which had a uniform temperature of 5 C. and left 

 until the water had been cooled to 7 C. They were examined 

 at regular intervals. At 16 there was no noticeable change in 

 any of the sponges. At n° all had a shriveled appearance, some 

 of the oscula were open slightly, and very slow currents coming 

 from them were barely visible. At io° no oscula could be found, 

 and at 7 the dermal membrane had completely shrunk in over 

 the body of all the sponges and no sign of activity could be 

 detected. The dishes were transferred to an incubator and 



