Reactions of Spojiges 3 1 



same level. After the whole apparatus was set up the water in 

 w^hich the sponge rested was deeply colored with methyl green. 

 The vessel with uncolored water was then lowered till the 

 difference in level between the water contained in it and in the 

 other vessel was sufficient to break through the ostial openings, 

 a state of affairs that could be recognized by the passage of the 

 deep bluish green water up one arm of the siphon. The differ- 

 ence \n level was then measured and in the eight trials that were 

 made it was found to be between ten and fifteen millimeters. 

 Thus the actual amount of resistance in the closed ostia is much 

 more than is necessary to hold in check a current whose maximum 

 suction is represented by a pressure of not over four millimeters of 

 water. I also attempted to get the resistance of a closed osculum. 

 Oscular tips were tied to the small end of the siphon tube, which 

 in this instance was made to carry colored water, and by raising 

 the reservoir on the colored-water side a pressure was sought at 

 which the osculum would open and discharge colored water. 

 But my experiments failed mostly because of leakage, probably 

 through the ostia near the osculum. They went far enough, 

 however, to assure me that the resistance of the osculum was 

 higher than that of the ostia. From these observations it is 

 quite evident that the currents produced by the choanocytes of 

 Stylotella are of such a strength that they can be readily held 

 in check by the ostia and the oscula, and that there is no mechan- 

 ical ground for suspecting that these currents could in any physi- 

 cal way endanger even the delicate structure of the sponge. 



The experiments with various stimuli had in many cases little 

 or no observable influence on the currents produced by the choan- 

 ocytes. The mechanical stimulation of the exterior of the sponge 

 had no effect on the current. In ether- and chloroform-water 

 all currents ceased, as might be expected from the well-known 

 inhibitory action of these drugs on cilia, etc. Strychnine appar- 

 ently increased the vigor of the current, whereas cocaine and 

 atropin seemed to have no effect upon it. Dilute seawater and 

 freshwater brought the current quickly to a standstill. Lack 

 of oxygen first accelerated and then retarded it. Cold caused it 

 to become slow, and excessive heat brought it to a standstill. 



