Reactions of sponges II 



so, tor, if a sponge after it has been dislodged, is left in the out- 

 side seawater, its oscula remain open. Change in illumination 

 was also suspected of bemg the cause of the contraction. But if 

 a sponge in its natural situation in full sunlight is suddenly shaded 

 to an extent not unlike the diffuse daylight of the laboratory, the 

 oscula still remam open. The reduction in the intensity of the 

 light, then, is not the cause of the contraction. After this the effects 

 of currents was tried, for, so far as could be judged, the chief 

 difference between the condition of the sponge in its usual habitat 

 and in the laboratory, aside from recent disturbance and illumina- 

 tion, was that in the first situation it was in moving seawater and 

 in the second it was in the same water standing still. An aqua- 

 rium with a free circulation of water was set up and sponges were 

 placed in this in such situations that they caught the full effects 

 of the current. The results were verv uniform. Sponges from the 

 exterior often arrived in the laboratory with many of their oscula 

 closed. On putting these specimens into the aquarium under a 

 strong current of seawater they almost invariably opened their 

 oscula within ten minutes. The following record from my 

 laboratory note-book will give a good idea of the character of 

 these changes. 



12:40 p.m. A sponge brought directly from the outside was 

 placed in the aquarium with a strong circulation of seawater. 

 Many of the oscula were closed. 



12:45. Oscula began opening. 



1:10. All oscula have been widely open for some time. Sea- 

 water current is now cut off. 



1:12. Many oscula are closing. 



I :i4. Most oscula are closed. Seawater current is now turned 

 on again. 



I :i8. Oscula have begun opening. 



1 :25. Most oscula are open. 



I ."39. Oscula remain open. 



This and many other similar experiments pointed to the impor- 

 tance of currents in keeping the oscula open, but this form of 

 experiment did not show what particular aspect of the current 

 caused the osculum to open or to remain open. Did the sponge 



