32 



G. H. Park 



arker 



Light, as might have been expected, did not alter it. So far as 

 these various stimuH change the current at all, they do so as one 

 would expect of them supposing that they acted directly on the 

 choanocytes and not through any intermediate structure. Never- 

 theless it cannot be said from the evidence presented that the 

 complete cessation of the current, as for instance in fresh water, 

 may not be due to the contraction of sphincters other than the 

 ostia and oscula rather than to direct action of the choanocytes. 



E. Coordiuatio}! of Reactions 



A comparison of the reactions of the oscula, ostia, and choan- 

 ocytes of Stylotella, as described in the preceding sections, can 

 best be made through a summary such as is contained in Table 2. 



The most marked feature brought out in Table 2 is the very 

 striking independence of the several reactive organs. Thus the 

 activity of the choanocytes, as indicated by the current they pro- 

 duce, is apparently quite independent of that ot the oscula or the 

 ostia and the only stimuli that have any effect on these cilia-like 

 organs are such as would be expected to influence them directly. 

 1 he oscula and ostia both possess sphincters that from a histolog- 

 ical standpoint are much alike in that they probably are a primi- 

 tive form of smooth muscle, a view supported by their reactions 

 to drugs, and yet they are influenced in totally different ways by 

 several stimuli, especially of a mechanical kind. This is so strik- 

 ing that under natural conditions one of these sets of apertures 

 may be found open when the other is closed. The contraction of 

 the common flesh is also quite independent of the ostia, for, though 

 these apertures are in a measure imbedded in this flesh, the latter 

 may be contracted when the ostia are open. The contraction of 

 the flesh and the closure of the oscula always take place together 

 when the sponge is in quiet water or exposed to the air, but that 

 this is probably a coincidence rather than evidence of a real phys- 

 iological interdependence is seen from the fact that the oscula 

 close in ether- and chloroform-water, though the common flesh does 

 not contract in these media. Thus the various motor elements 

 in Stylotella seem to be as independent of one another as the several 

 parts of a single animal can well be. 



