46 THE ELEMENTARY NERVOUS SYSTEM 



was tied into the osculum of this sponge, and the sponge 

 and tube submerged in an aquarium. The flow of water 

 through the tube was then determined by measuring the 

 velocity of floating particles, such as grains of carmine, 

 that were carried up the tube by the water current. This 

 proved to be very nearly 4 millimeters a second. As the 

 diameter of the glass tube was 17 millimeters, the osculum 

 must have discharged a little over 0.9 of a cubic centimeter 

 of water a second. At this rate the discharge would 

 amount to some 78 liters a day. As an ordinary Spino- 

 sella may have as many as twenty such oscula, a colony 

 such as this would have to pass through its substance in 

 a day about 1575 liters of seawater, or over 45 gallons. 

 Sponge currents, therefore, are considerable in volume 

 but low in pressure (Parker, 1914 c). 



This lowness in pressure, which is rather in contrast 

 with the former belief as to the character of these cur- 

 rents, is favorable for their easy control by the closing 

 and opening devices at the dermal pores and oscula. The 

 adequacy of these devices has been tested in only one in- 

 stance, the dermal pores of Stylotella. A finger of this 

 sponge, in which the dermal pores were closed, was tied to 

 the small end of a glass tube which was bent in the form 

 of a siphon and was so placed that the end carrying the 

 sponge was in one vessel of water and the other end, quite 

 free, was in another vessel of water (Fig. 12). The water 

 in these two vessels was kept at the same level. After the 

 whole apparatus was set up, the water in which the sponge 

 rested was deeply colored with methyl green. The ves- 

 sel with uncolored water was then lowered till the differ- 

 ence in level between the water contained in it and in tli< i 

 other vessel was sufficient to break through the pores, 

 a state of affairs that could be recognized by the passage 



