SPONGES 39 



removal of these by a current of water would the oscula 

 open, or did the current carry oxygen to the sponge or 

 act in a purely mechanical way to induce the opening of 

 the oscula? To test these matters the following simple 

 experiment was tried. Three cylindrical glass aquaria of 

 considerable size were placed at three levels so that the 

 water from the uppermost aquarium could be siphoned 

 freely into the intermediate one, from which the water 

 overflowed into the third. Having filled the apparatus 

 with seawater, it was possible to keep it running continu- 

 ously with the same seawater by returning that which 

 collected in the third or lowest aquarium to the upper- 

 most one. If, now, the current of seawater carried away 

 excretions from the sponge or brought oxygen to it and 

 these operations had anything to do with the opening of 

 the oscula, the use of the same water over and over again 

 ought soon to bring on a condition that would no longer 

 cause the oscula to open. But sponges placed in the cur- 

 rent of the middle aquarium remained with their oscula 

 open for hours in seawater that had been used many times 

 over. Moreover, the oscula closed quickly when the cur- 

 rent was cut off and reopened soon after it was started 

 again. It, therefore, appears that the mechanical stimu- 

 lation of a current of water is an effective means of open- 

 ing or keeping open the oscula of Stylotella. 



These first experiments were made on whole colonies 

 of Stylotella and only the general condition of the oscula 

 was recorded. It was desirable, however, to ascertain 

 what part of the sponge must be exposed to the current 

 to induce an opening of the osculum or the reverse. To 

 test this question a colony of Stylotella was placed in a 

 strong current of seawater and, when the oscula were well 

 opened, a glass tube was lowered over a vertical finger 



