Characteristics 



CHAPTER XV 

 THE SPONGES Subkingdom PORIFERA 



THERE are about two thousand species of sponges known, which 

 range in size from a pin's head to masses several feet in height, and 

 vary in weight from a grain to over a hundred pounds. They assume an endless 

 variety of shapes, such as cups, vases, spheres, tubes, branched tree-like growths, 

 etc., but are often shapeless. When alive, they are of all colors, and their con- 

 sistency may be soft and glutinous, fleshy, leathery, or stony. They are found in 

 all seas, and in all depths from the shore margin to several miles deep, and certain 

 species occur in fresh waters all over the globe. About three hundred species have 

 been found round the coasts of Britain. Aristotle was the first to give a scientific 

 account of sponges. He considered that they were either animals, or organisms 

 transitional between plants and animals, and that they possessed sensation, since 

 they shrank when torn from the rocks. He classified the kinds then known, and 





BREAD-CRUMB SPONGE, SHOWING CURRENTS ENTERING SURFACE AND LEAVING BY OSCULES. 



asserted that the animals often found in the cavities of sponges were intruders, 

 and did not make the sponges;' further, he distinguished the large holes on the 

 surface of certain species from the small ones, and thought that water was sucked 

 in by the former. 



From the time of Aristotle till 1762 little was recorded, but in that year Ellis 

 published his observations on the bread-crumb sponge, a British species forming 

 fleshy masses or crusts of a yellow or greenish hue. This sponge envelopes the 

 stems of seaweeds, or incrusts rocks and stones; wh&n growing on seaweeds it 

 forms cake-like masses with a level surface, but when iucrusting rocks the surface 

 is covered with small cones resembling miniature volcanic craters. The surface 

 between the craters exhibits a very fine gauze-like pattern; and, by careful 

 inspection, groups of minute pores will be seen perforating -the meshes. The large 



