44 SPONGES 



water is the most suitable agent for carrying food. The 

 sponge is furnished with cells bearing flagella which, by 

 their movements, maintain currents of water laden with 

 food. 



Economic importance of the sponges. — A few sponges 

 have formed the habit of boring into limestone rock and 

 into the shells of certain mollusks, but the destructiveness 

 of these few is probably not great. On the other hand, 

 the commercial trade in sponges is large. The sponge 

 fisheries in the Mediterranean Sea give employment to 

 thousands of people, and the receipts from sponges sent to 

 foreign markets amount to thousands of dollars annually. 

 The value of the sponges handled in Trieste, alone, in one 

 year, amounts to nearly two hundred thousand dollars, 

 and the demand for sponges is continually increasing. 

 Moreover, there are the sponges from the Bahamas, Red 

 Sea, and West Indies that must be taken into account in 

 any reliable estimate of the economic value of sponges. 



CLASSIFICATION OF THE EXAMPLES 



Branch II — Porifera. 

 Class — Porifera. 



Ascetta primordialis — Simple sponge. 

 Grantia species — Simple sponge. 

 Euplectella aspergillum — Venus's basket. 

 Hyalonema species — Glass-rope sponge. 



