II r DBA 



263 



from a central one. This is the case, for example, in the bath- 

 sponges. A small bath-sponge is composed of the skeleton of 

 only a single individual, whereas the larger sponges may be com- 



Fici. 253. — Stjcon gelatinosum. A portion slighth' nuignified : one c^'linder 

 (that to the right) l:)isected longitudinaUy to show the central stomach- 

 cavity opening on the exterior by the oseulum, and the position of the in- 

 current and radial canals ; the former indicated by the Ijlacl: 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, oseulum. 



posed of half a dozen or more zooids, the number of which may 

 be determined by counting the number of large openings in the 

 sponge. The soft living matter may easily be removed from 

 the skeleton, and this is regularly done in preparing the sponges 

 used in commerce. Our common bath-sponges come from 



