34 SPONGID.E. 



anew by Dr. Bowerbank, from whose observations, 

 made, for the most part, on the common fresh- 

 water Sponge, the follo\ving conclusions seem dedu- 

 cible, viz. : — 



1. That the circulatory action is, in all probabi- 



lity, due to the presence of vibratile cilia. 



2. That these cilia (if present) are situated, not 



around the oscula or pores, but rather within 

 the larger excurrent canals which run im- 

 mediately beneath what may be termed the 

 " dermal membrane " of the Sponge. 



3. That the circulatory action is, to a certain 



extent, periodical, continuing for a sufficient 

 length of time to enable nutrient particles 

 to be conveyed to all parts of the interior of 

 the Sponge, after which it becomes languid 

 for a while, to be again resumed, when its 

 performance is called for to supply the ne- 

 cessities of the organism. 



And further, it has been proved, 



4. That the living animal possesses the power 



of opening and closing its oscula at plea- 

 sure ; 



5. That the several oscula may act more or less 



independently of one another ; and 



6. That new oscula may be formed, if required, 



any^vhere in the course of the larger excurrent 

 canals. 



It is obvious that the above currents may be 

 employed, not merely in the conveyance of food, 

 but likewise in the removal of effete matter. 

 They contribute, moreover, to the general aeration 

 of the entire animal, presenting us, it may be said, 



