62 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



them with little or no success. The United States Bureau 

 of Fisheries has found a method that it believes to be practi- 

 cable. Live sponges are cut into small pieces which are 

 fastened on some firm support and placed in suitable places. 

 In from four to six years these fragments grow to a good 

 marketable size. 



Boring Sponges. Among the most interesting and impor- 

 tant of the sponges are the boring sponges which live on shells, 

 spreading over the surface at first but eventually penetrating 

 the shell in every direction, completely honeycombing it, and 

 causing it to break up. They thus help to dispose of the shells 

 of dead molluscs which would otherwise accumulate in vast 

 quantities. They also attack shells in which the animals are 

 still living and by boring through the shell greatly irritate the 

 host which must constantly secrete new shell to close up the 

 holes made by the intruder. These boring sponges are often 

 serious pests in the oyster beds. The pearl-shell fishermen 

 sometimes find some of their largest and otherwise finest shells 

 completely ruined by the work of some of them. 



Classification. There is only one class belonging to the 

 branch Porifera (L. porus, pore; fero, to bear) and that, too, 

 is called Porifera. It is divided into two sub-classes, the 

 Calcarea, including those sponges with a skeleton of calcareous 

 spicules, and the Non-calcarea, with the skeleton either absent 

 or composed of spong in fibers or of siliceous spicules. Grantia 

 is an example of the sub-class Calcarea; the commercial 

 sponges, the boring sponges, and indeed most of the others, 

 belong to the Non-calcarea. 



