SPONGES 



47 



of the deep greenish water up one arm of the siphon. The 

 difference in level was then measured and in eight trials 

 it was found to be between 10 and 15 millimeters. Thus 

 the actual resistance of the closed pores is much more 

 than is necessary to hold in check a current whose maxi- 



FIG. 12. Diagram of the apparatus to test the strength of the dermal pores of Stylotella. 

 A finger of Stylotella with closed pores was attached to a glass siphon tube connecting two 

 vessels of seawater which in the beginning were at the same level. After the apparatus was 

 in position some methyl green was dissolved in the water of the vessel in which the finger 

 was The other vessel was then lowered till the difference in pressure between the water in 

 the two vessels caused that in the first vessel to break through the pores of the sponge and 

 pass over into the other vessel as was indicated by the appearance of the colored water in 

 the siphon tube. The difference in the levels of the water in the two vessels was then meas- 

 ured and thus the pressure necessary to open the dermal pores of the sponge was determined. 



mum suction is represented by a pressure of not over 

 4 millimeters of water (Parker, 1910 a). 



Notwithstanding the fact that the opening and clos- 

 ing mechanisms of the dermal pores and oscula in sponges 

 involve independent effectors in the form of primitive 

 muscle cells, it would be quite erroneous to ascribe to 

 these animals a complete absence of transmission. It 

 has already been pointed out that if an injury, for in- 



