SPONGES 33 



cavities. These cavities form a set of intercommunicat- 

 ing spaces over the whole surface of the sponge, and the 

 currents that set into them at the cut end depend largely 

 upon the action of the choanocytes. If, now, no inward 

 currents can be detected at the dermal pores but currents 

 can still be seen to enter the subdermal cavities at their 

 cut ends, it is clear that the absence of the currents at the 

 pore entrances is due to the closure of the pores, and not 

 to the cessation of the choanocytes. In this way the 

 entrance of currents into the dermal pores can be used to 

 indicate the open condition of the pores, and their ab- 

 sence, when coupled with currents into the subdermal 

 spaces, to indicate the closed condition of the pores. 



The means of inducing the opening and closing of the 

 dermal pores in Stylotella as tested on preparations such 

 as those described in the last paragraph were found to 

 be numerous. The pores closed on injury inflicted in the 

 neighborhood of the surface under inspection. They also 

 closed when the seawater passing through them contained 

 a small amount of ether (1/200), chloroform (1/200), 

 strychnine (1/15,000), or cocaine (1/1000). They were 

 apparently unaffected by mechanical stimulation, except 

 injury, by temperatures as low as 9 degrees centigrade 

 and by light. They opened in solution of atropin 

 (1/1000), of weak cocaine (1/10,000), in dilute seawater, 

 deoxygenated seawater, and warm seawater, 35 degrees 

 centigrade (Parker, 1910 a). 



The mechanism of opening and closing the dermal 

 pores is more complex than has generally been assumed 

 and has been very adequately described by Wilson (1910). 

 In Stylotella, according to this author, the membrane cov- 

 ering each subdermal cavity and containing the pores, 



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