434 EVENINGS AT THE MICROSCOPE 



These openings are sections of so many canals, by 

 which the whole substance of a sponge is permeated. The 

 surface is perforated with minute pores, at which the sur- 

 rounding water enters on all sides. These presently unite 

 into slender pipes, which, irregularly meandering, are con- 

 tinually uniting into larger and yet larger canals ; of which 

 the greater open spaces that you see are the oblique di- 

 visions. These have certain outlets, called oscula, on the 

 surface, from which the stream is poured out that has thus 

 made the grand tour of the whole interior. Such oscula, 

 as you perceive on the remainder of the Halichondria, are 

 usually raised on slight eminences; and resemble, espe- 

 cially when in living action, miniature volcanoes, vomiting 

 torrents of water and granules of effete matter, instead of 

 fire and ashes. 



During life these granules were much more diffused, 

 and formed a considerable portion of the living flesh, the 

 remainder being composed of a glairy sarcode, almost 

 fluid. The whole was maintained in position by the solid 

 spicula of flint, which you see abundantly in this slice. 

 These take a curious form, exactly that of the pins which 

 we use on our dressing tables; each consisting of a cylin- 

 drical slender rod, pointed at one end, and at the other 

 surmounted by a globular head, the whole formed of glass 

 flint glass literally. You see them bristling all round 

 the edge of the section, being stuck into the surface of the 

 sponge, exactly as pins are loosely stuck into a pin-cush- 

 ion. The heads and points, too, project into the cavities; 

 more, however, than they did during life, for you must 

 make allowance for the shrinking of the soft parts; and 

 thus you perceive how the whole structure is permeated 

 by these glassy pins, which seem to be entangled together 



