VI. SPONGES 

 Branch II. — Porifera (porop, pores; ferens, bearing) 



All sponges live in water, either fresh or salt. The fresh- 

 water sponges may be found in rivers, lakes, ponds, etc., 

 probably in every country in the world. The marine 

 sponges are very widely distributed m the sea and occur at 

 nearly all depths, from the shallow to the very deep parts 

 of the ocean. In some parts of the sea they are exceedingly 

 abundant. They are of multitudinous forms, intlividuals 

 of the sanre species varying greatly in shape. Some are 

 flat, some are globular, some are treelike in shape, others 

 are vasclike in form, while some are cylindrical. This va- 

 riation in shape is due largely to the fact that they are easily 

 modified b}' surrounding conditions. A change in current 

 or a change in the character or shape of the sea bottom mil 

 almost surely bring about a change in the shape of these 

 animals. \^nien the young marine sponges are first hatched 

 from the egg, they are, for a time, free, and they can move 

 al)out through the water. They soon become attached 

 and for the rest of their lives remain stationary. Hence 

 sponges may be said to be fixed animals. 



Structure of a simple sponge. — The simplest sponge 

 that we know anything about is vase-shaped, with the 

 lower end conti'actod into a sort of stalk by which the ani- 

 n)al is attached. Generally speaking, the body is a hollow 

 cylinder, closed at the lower end but open at the opposite, 



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