I56 GEORGE T. MCNAIR. 



brought about by a contraction of longitudinal fibers, but it 

 could not be definitely demonstrated. 1 



Effects of Currents of Water on the Osculum. 



Potts ('87) makes the statement that he found E. fluviatilis 

 in both quiet and running water. It seems to grow best in 

 ponds of quiet water, but very fine specimens are found on the 

 under side of rocks in rapids or at the base of water falls where 

 the river current is the swiftest. 



To get an idea of the effects of water currents, a few sponges 

 were placed in a flat dish containing about a quart of water and 

 left over night. The next morning the oscula were still expanded, 

 and, by watching the movements of tiny particles of suspended 

 material in the water, steady currents could be seen flowing 

 through them. This test was repeated with the same results. 

 It was noticed, however, that if the sponges were left in such a 

 dish of unchanged water much longer than a day they gradually 

 became less active and in many cases soon died. 



To determine the effect of a swift current, a glass tube was 

 connected with the water tank and placed in one side of a dish 

 containing the sponges. The water was turned on at full force 

 and left running for about four hours. After transferring the 

 sponges to a watch glass for observation (without taking them 

 from the water) it was found that the entire chimney had con- 

 tracted until it was almost flat, but that the mouth of the osculum 

 was wide open and currents of water were coming out. The 

 following illustration shows the extent of the contraction of 

 the chimney. 



Fig. 2. A chimney before and after a strong current of water had been applied, 

 showing the extent of the contraction. 



1 See, E. A. Minchin, Lankester's "Treatise on Zoology," p. 44. 



