PHYLUM PORIFERA 



77 



cylinders (Fig. 34), all connected together at the base, 

 where it is attached to the surface of seaweeds, rocks, or 

 other solid bodies submerged 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 — the inhalant pores. At the free end of each of the 

 cylindrical branches is a small but distinct opening, sur- 

 rounded by what appears like a delicate fringe. When the 

 branches are bisected longitudinally (Fig. 35), it is found 

 that the terminal openings (o) lead into narrow passages, 



Fig. 34. — Sycon gelatinosum. Entire sponge, consisting of a group 

 of branching cylinders (natural size). 



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 pas- 

 sages thus forming a communicating system. On the wall of 

 the passages are numerous 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 pas- 

 sages the paragastric cavities. If the living Sycon is placed 

 in sea-water with which has been mixed some carmine pow- 

 der, it will be noticed that the minute particles of the 

 carmine seem to be attracted towards the surface of the 



