SECT. Ill 



PHYLUM PORIFERA 



77 



merged in the sea. It is flexible, though of tolerably firm 

 consistency. On the outer surface are to be detected, under 

 the microscope, groups of minute pores fo& inhalant pores. 

 At the free end of each of the cylindrical branches is a 

 small but distinct opening, surrounded by what appears 



FIG. 33. Sycon gelatinosum. Entire sponge, consisting of a group of 

 branching cylinders (natural size). 



like a delicate fringe. When the branches are bisected 

 longitudinally (Fig. 34), it is found that the terminal open- 

 ings (o) lead into narrow passages, wide enough to admit a 

 stout pin, running through the axis of the cylinders ; and 

 the passages in the interior of the various branches join 

 where the branches join the passages thus forming a com- 

 municating system. On the wall of the passages are numer- 

 ous fine apertures which require a strong lens for their 

 detection. The larger apertures at the ends of the branches 

 are the oscula of the sponge, the passages the paragastric 

 cavities. If the living Sycon is placed in sea-water with 

 which some carmine powder has been mixed, it will be 

 noticed that the minute particles of the carmine seem to be 

 attracted towards the surface of the sponge, and will often 

 be seen to pass into its substance through the minute in- 

 halant pores already mentioned as occurring in groups 



