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MANUAL OF ZOOLOGY 



sponge, and will often be seen to pass into its substance 

 through the minute pores already mentioned as occurring in 

 groups between the elevations on the outer surface. This 

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



Fig. 35. — Sycon gelatinosum. A portion slightly magnified; one cylinder (that 

 to the right) hisected 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; o, osculum. 



into the interior of the sponge through these minute open- 

 ings dotted over the surface ; and the movement of the 

 floating particles shows that a current is at the same time 

 flowing out of each of the oscula. A constant circulation of 



