CHAPTER III 



SPONGES (Continued) 



THE oscula of sponges are, in comparison with their 

 pores, relatively large openings and hence they admit of 

 experimental treatment such as is not possible with the 

 pores. In Stylotella each finger ordinarily carries at its 

 free end a single large osculum. The opening and clos- 

 ing of this osculum is the most obvious response of this 

 sponge. If a colony under ordinary conditions is exam- 

 ined, some of the oscula will almost certainly be found 

 closed, though the majority will be widely open. If a 

 small colony is closely inspected under a low power of the 

 microscope, the open oscula will be seen to emit a large 

 number of minute particles indicating that a current is 

 setting out through these openings. In what seem to be 

 closed oscula a minute but otherwise similar current can 

 often be detected, showing that they are really not closed. 

 Some oscula, however, show absolutely no current, 

 though it has been invariably found that when in such 

 cases the oscular tip is cut off, the current can be seen 

 almost instantly and it is, therefore, concluded that at 

 times the oscula do close completely and thus check ab- 

 solutely the current that ordinarily passes through them. 



In order to get some idea of the natural movements 

 of the oscula, a vigorous colony of Stylotella was isolated 

 and three of its oscula were kept under approximately 

 hourly observation for three days. The results of these 

 observations are summarized in Table 1. 



37 



