328 THE WEALTH OF THE SEA 



which leads to a vent or opening in the skin. Water 

 carrying food and oxygen enters the pores and is 

 drawn through the canals to the pear-shaped cham- 

 ber and then expelled through the vents. 



Relatively little is known concerning the life of the 

 sponge. The young sponges which are hatched from 

 eggs are minute free-swimming organisms. When 

 still very small, they settle to the bottom and attach 

 themselves to some solid object, where they live the 

 rest of their lives. The shape, size, and outward 

 appearance of a sponge depends to a large extent 

 upon its environment. Sponges transplanted to 

 different waters often change their general 

 characteristics. Many sponges can tolerate exposure 

 to the air for considerable periods and thus are able 

 to grow at the low-water mark. They are found in 

 water up to six hundred feet in depth. 



The skeleton of the commercial sponge consists 

 chiefly of spongin, a protein related to conchiolin, 

 which is found in the shells of moUusks, and fibroin 

 and sericin, the principal constituents of silk. Cer- 

 tain compounds of sponges contain a relatively large 

 amount of iodine in organic combination. 



Methods of Fishing * 



Probably the earliest method of taking sponges 

 was that of hooking or cutting them from the bot- 

 tom while wading in shallow water along the sea- 

 shore. Even to-day in the southern part of Tunisia 

 the natives follow a similar method, wading until they 

 find a sponge, detaching it with their toes, and then 

 kicking it within reach of their hands. 



