38 THE ELEMENTARY NERVOUS SYSTEM 



TABLE 1 



PERIODS OF TIME IN HOURS AND MINUTES DURING WHICH IN THE COURSE op 

 THREE DAYS OSCULA 1, 2 AND 3 WERE OPEN OR CLOSED 



Since the three oscula whose conditions are recorded 

 in Table 1 were on the same colony and near together and 

 were exposed to almost identical surroundings, the fact 

 that osculum 1 was closed on the average one hour in 

 every two and a half, while oscula 2 and 3 were closed 

 only one hour in eveiy eighteen, must be attributed to 

 the difference in constitution of osculum 1 as contrasted 

 with that of the other two. The condition of general 

 openness as exemplified by oscula 2 and 3 is doubtless 

 typical for these organs. At least in any vigorous sponge 

 under normal conditions, the majority of the oscula will 

 be found open much of the time. 



The closure of the oscula can be brought about in a 

 variety of ways. When a colony of Stylotella is trans- 

 ferred from running water in the exterior to a collecting 

 bucket of quiet water, the oscula commonly close. They 

 reopen on being brought again into running water. This 

 and many other similar experiments pointed to the im- 

 portance 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 give out excretions that in quiet 

 water gathered to such an extent in its immediate neigh- 

 borhood as to cause its oscula to close and only on the 



