20 G. H. Parker 



si/e of the ostia makes a direct determination of their condition 

 almost impossible and consequently the presence or absence of a 

 current of water through them was taken as an indication of their 

 state. The demonstration of this current has been accomplished 

 from the earliest tim.es (Carter, '56, Lieberkiihn, '56, Bow^erbank, 

 '58) by the addition to the water of some such substances as car- 

 mine, starch, or indigo, whose particles could then be followed as 

 they were carried in the moving water. Latterly this method has 

 been severely criticised bv von Lendenfeld ('89, p. 592), w^ho 

 claims that even these small suspended particles mechanically 

 stimulate the sponge and cause it to close its ostia. Von Lenden- 

 feld has used milk as an indicator and has found no objection to it. 

 With Stylotella it is easy to demonstrate the ostial currents with 

 carmine, etc., and so far as I could discern this material could be 

 used without causing partial closure of these apertures. In fact I 

 must agree with Bidder ('96, p. 32) that the carmine particles 

 seemed to have no effect whatever on the ostia, bat were swept 

 into the interior of the sponge with great freedom for hours at a 

 time. It must, however, be confessed that not only carmine but 

 even milk is an unnatural substance for a sponge and as Stylotella 

 lives in water that ordinarily contains much fine suspended 

 material, I found it necessary only to watch this substance to gain 

 all the information that was needed as to the direction of ostial cur- 

 rents, their strength, etc. 



In testing the ostia I usually pinned a finger of sponge under the 

 microscope in a small glass aquarium so arranged that a continu- 

 ous current of seawater could be kept running through it, and by 

 watching the suspended particles along the sides of such a prepara- 

 tion under a magnification of about ninety diameters, it was com- 

 paratively easy to ascertain w^hether the ostial currents were 

 running or not. Asa rule the objective of the microscope was used 

 as an immersion lens and plunged under the surface of the sea- 

 water. In making these observations it was, however, necessary 

 for the time being to stop the current of seaw^ater that was running 

 through the small reservoir, otherwise the movement of the sus- 

 pended particles over the surface of the sponge was so rapid that 

 it was impossible to tell whether they entered an ostium or glided 



