30 THE ELEMENTARY NERVOUS SYSTEM 



The opening and closing of the dermal pores in Stylo- 

 teUa has been observed directly in living preparations by 

 Wilson (1910), whose account will be referred to pres- 

 ently. In the following experimental tests the presence 

 or absence of currents was used as an indication of the 

 state of the pores. The demonstration of these currents 

 has been accomplished from the earliest times by the ad- 



Fio. 5. Radial portion of a transverse section of Stylotella; the flesh of the sponge is 

 dotted, the cavities are undotted; on the extreme left is the dermal membrane pierced by 

 two pores p that lead into a large subdermal space s, from which incurrent canals i lead to 

 the flagellated chambers /, which in turn open by excurrent canals e into the cloaca c. 



ditiou to the water of some such substances as carmine, 

 starch, or indigo, whose particles could then be followed 

 as they were carried in the moving water. Latterly this 

 method has been severely criticized by von Lendenfeld 

 (1889), who claims that even these small suspended par- 

 ticles mechanically stimulate the sponge and cause it to 

 close its pores. Von Lendenfeld used milk as an indi- 

 cator and found no objection to it. With Stylo fell a it is 

 easy to demonstrate the pore currents with can nine and 

 the like, and, so far as could be discerned, this material 

 could be used without causing partial closure of these 

 apertures. In fact, as stated by Bidder (1890), carmine 

 particles seemed to have no effect whatever on the dermal 

 pores, but were swept into the interior of the sponge with 



