SPONGE WEAVERS. 129 



open, and pouring out with considerable force each its 

 stream of the outflowing (excurrent) fluid (fig. 19) ; 

 this vigorous action will sometimes be continued for 

 several hours, and then either gently subside, or 

 abruptly terminate. Occasionally a cessation of the 

 action may be observed in some of the oscula, while 

 in others it is proceeding in its full vigour, and 

 sometimes it will be suddenly renewed, for a brief 



FIG. 19. PIECE OF SPONGE MAGNIFIED. 



period, in those in which it had apparently ceased. 

 These vacillations in the performance of its functions 

 is always indicative of an approaching cessation of 

 its vigorous action. When the vivid expulsion of 

 the water has ceased, the aspect of the oscula under- 

 goes a considerable change ; some of the smaller 

 ones gradually close entirely, while in the large 



K 



