Reactions of Sponges 9 



Although the larger apertures, including the osculum, possess 

 well defined sphincters by which they are closed, I have never been 

 able to find in Stylotella systems of radiating fibers by which they 

 might be opened. Now and then I have seen what seemed to be 

 slight radiating systems, but they were always associated with 

 closed or parti}' closed openings and might perfectly well have 

 owed their origin to the mechanical stretching of the elastic 

 tissue m the neighborhood of a sphincter. I am inclined to 

 believe therefore that the myocytic sphincters in Stylotella work 

 against the general elasticity of the body tissue, which may have a 

 slight radial arrangement in their neighborhood, rather than that 

 thev oppose a well defined system of radial myocytes. The 

 absence of radial fibers in many sponges in which sphincters occur 

 has been noted by Minchin ('00, p. 46). 



4. REACTIONS OF STYLOTELLA 



A . Movements of the Oscida 



The opening and closing of the oscula in Stylotella, as already 

 mentioned is the most obvious of the responses of this sponge. 

 If a colony under ordinary conditions is examined, 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 reallv not closed. Some oscula, 

 however, show absolutely no current, though I have invariably 

 found that when in such cases the oscular tip was cut off, the 

 current almost instantly could be seen, and I believe, theref re, 

 that the oscula do close completely and thus check absolutely 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 I. 



