20 GUIDE TO THE CORAL GALLERY. 



PORIFEEA [SPONGES]. 



[The High Cases are indicated by Roman numerals and the shelves of the 



same by Arabic numerals.] 



Introduction. 



High Cases The term " sponge " is popularly associated solely with the soft 



Table Cases elastic bath sponge, hut a glance at the Cases will show that, in 



1 and 2 a, b. zoology, the word has a much wider meaning, some " sponges " 



being of stony hardness, others leathery, others again like spun glass. 



In life, the bath sponge is tough and fleshy, and covered with a 

 black skin (Case I., specimen in fluid). A section (Fig. 18) shows 

 a light-coloured flesh in which no trace of the horny skeleton, 

 commonly known as the sponge, is apparent ; to obtain this the 

 skin and flesh are macerated off, leaving the more resistant skeleton. 



It would be instructive here to notice the glassy skeleton of 

 EupUctella aspergillum, or Yenus' Flower-Basket (Cases III. 2), aud a 

 complete specimen of the same in fluid (Table Case 2a) ; here again 

 the skeleton is concealed by the soft tissues. The dried specimen of 

 EuplecteUa imperialis (Case III. 3) shows the fluffy-looking soft 

 tissues above and the denuded skeleton below. 



Many sp-jcimens, especially those in Cases lY.-VL, do not 

 materially ditt'er, excepting in colour, from their appearance in life. 



The position of Sponges in the Animal Kingdom is above the 

 Protozoa or Simplest Animals and near the Coelentera (Zoophytes, 

 Corals, &c.). 



To give some idea of the structure of a sponge, a brief account is 

 given of Ealkliondria imnkea, the Crumb-of -Bread Sponge, common 

 round the British coast (Case lY. 3). 



This sponge forms yellow or greenish crusts on rocks, or shapeless 

 masses round the stems of sea-weeds. The surface of incrusting 

 specimens is usually covered with crater-like orifices termed oscules. 

 On closely observing living specimens in a large vessel of sea-water, 

 currents, rendered visible by debris, Avill be seen coming out of the 

 oscules ; a little indigo or carmine will serve to render the currents 

 still more apparent. 



