166 THE BOTTOM OF THE SEA. 



necessary to its development. The creature has lost 

 its mobility, and become to all appearance an inert 

 mass. It resembles a most irregular and ill-formed 

 vegetable ; the holes begin to bristle with horny fila- 

 ments entangled one in the other, and constituting a 

 kind of solid carpentry. By-and-by other siliceous 

 or calcareous filaments mingle with the first, and fill 

 up the cavities which had been left among them. 

 The forms of these are most varied according to the 

 species to which they belong, and often spiculse very 

 different in their aspect are combined in the same 

 individual. They are generally so small that their 

 nature is only discovered by means of the microscope. 

 With its aid some are seen to be shaped like har- 

 poons, some like stakes with pointed ends, some like 

 stars or crystal knots of the most curious forms. 



The various species of sponge are distinguished by 

 their tissue being more or less close, more or less 

 crooked . Sometimes their mass is surrounded in nearly 

 every part with a siliceous or calcareous envelope. 

 The coasts of Europe furnish some sponges of this kind, 

 but the most remarkable come from the sea of the 

 Antilles and from that of Japan. Sometimes the 

 siliceous spiculae fill the tissues so completely that the 

 sponge serves as a polishing material. The use, how- 

 ever, to which the sponge is generally destined is 

 suggested by the facility with which it takes up 



