CHAPTER VI 



SPOXGES 



Porifera 



Form and habits of sponges. — To most people the word 

 sponge means bath-sponge. To others it calls to mind the 

 sulphur-sponges of the New England coast or the glassy 

 lace work of the Venus' fiow^er-basket of tropical waters. At 

 any rate it probably suggests salt water and this association 

 is quite natural, for salt water sponges exist in an infinite 

 variety of shape and hue. There are hardly more than 40 

 to 50 species of fresh water sponges yet known in North Ameri- 

 ca. They are dull-colored, greenish, often moss-like (PI. X), 

 usually not seen and even if they are noticed, their real 

 identity is not suspected. 



Fresh and salt water sponges both consist of colonies of 

 animals which are living together. In close view a fresh 

 water sponge and a piece of bath-sponge look much alike. 

 Both have uneven hubbly surfaces peppered with thousands 

 of holes, the pores which have given the name Porifera to 

 the sponge group (PI. VI, i). Leading from these pores is a 

 network of canals and chambers in which food and water 

 pass through the soft body tissue of the sponge. All sponges 

 are alike in having a lattice-like supporting framework or 

 skeleton upon which their soft tissues are arranged. This 

 skeleton may be tough and elastic — the spongin of the bath- 

 sponge; glassy — of silicious spicules like the glass sponge; 



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