SPONGES. 25 



living, is the seat of all the animal life which the Sponge can 

 boast. It secretes and deposits the substance of the skeleton, 

 and keeps up some kind of action exerted in every part of 

 the body, which, although scarcely perceptible, serves to 

 produce a continuous succession of currents in the surround- 

 ing fluids. The living Sponge can be seen, if placed in a 

 glass and examined by a microscope, to imbibe and expel 

 currents of water, which appear to pass into the smaller 

 meshes of network, carrying nourishment into all the re- 

 cesses of the body, and then to be ejected by the larger 

 holes appearing on the surface ; and this is all the creature 

 shows of animated existence, for the filmy flesh does not 

 contract when touched, or show any other sign of sensibility. 

 The propagation of Sponges is curious ; for at the proper 

 season many minute buds may be found adhering to the 

 sides of the passages or openings. These buds are the em- 

 bryos of the Sponge, gradually increasing in size they become 

 clothed with movable cilia, and when fully developed fall 

 off, and, becoming detached, enjoy a locomotive freedom un- 

 known to their parent. Their motion is effected by means 

 of the cilia, which continue vibrating and produce a current 

 round the little body, which impels it forwards. It is not 

 long a wanderer in the " world of waters )^ and whether it 



