PHYLUM PORIFERA SPONGES 161 



body capable of doing work), but has no nervous mechanism 

 to control them and they respond when stimulated directly. 

 In more specialized animals the nervous system has more or 

 less complete control of effectors the receptors (eye, ear, 

 etc.) receive stimuli and send impulses to the central nervous 

 system, which in turn sets off appropriate effectors. 



SPONGE FISHERY 



The total value of the sponge fisheries of the world 

 amounts to about $3,500,000 annually. In the year 1907 

 sponges were imported to the United States to the value of 

 $488,426 and exports during the same year amounted to 

 $144,354. In 1908, on the Florida fishing grounds alone, 

 622,489 pounds of sponges were captured and sold for 

 $548,876. The growing importance of the sponge fisheries 

 has led the federal government to make studies of the best 

 methods of propagation and fishing. 



It is possible to raise sponges from slips, like plants, and 

 this has been made use of in a commercial way. Selected 

 individuals of good quality are cut up and the pieces placed 

 on the tips of sharp stakes attached to a frame. The frame 

 is lowered to the bottom of the ocean, left for a year or two, 

 and raised again. If all has gone well, the " slips " have 

 grown to marketable size and are of good shape (Fig. 66). 

 It is possible to graft fragments of fine sponges on the at- 

 tached growing bases of Bother indviduals of poor quality. 

 The two sponges fuse and a vigorous growth of the desirable 

 portipn is thus obtained. 



Sponges are usually collected by hooking or diving. In 

 the first method one man rows a boat and another uses a 

 rake-like hook to tear the sponges from their attachments. 

 In the second, divers go down and cut the sponges off the 

 bottom by hand. Along the shores of the United States 

 fishers usually, wear diving suits, but in the Mediterranean 

 and other seas they are more often nude. In some places 

 dredges are used in capturing sponges, but they are un- 



