MANUAL OF ZOOLOGY 



SECT. 



between the elevations on the outer surface. This would 

 appear to be due to the passage of a current of water into the 

 interior of the sponge through these minute openings dotted 

 over the surface ; and the movement of the floating particles 



FIG. 34. Sycon gelatinosum. A portion slightly magnified ; one cylinder (that 

 to the right) bisected longitudinally to show the central paragastric cavity 

 opening on the exterior by the osculum, and the position of the incurrent and 

 radial canals ; the former indicated by the black bands, the latter dotted, ip 

 marks the position of three of the groups of inhalant pores at the outer ends of 

 the incurrent canals ; <?, osculum. 



shows that a current is at the same time flowing out 

 of each of the oscula. A constant circulation of water 

 is thus carried on currents moved by some invisible 



