CHAPTER XY. 
The Sponoes,- 
-Subkingdom PORXFERA. 
There are about two thousand species of sponges known, which 
ClidirdiCt)6rist)ics ^ ^ 
’ 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 colours, and 
their consistency 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 asserted that the animals often found in the cavities of sponges 
were intruders, and did not make the sponges; further, he distinguished the 
BREAD-CRUMB SPONGE, SHOWING CURRENTS ENTERING SURFACE AND LEAVING BY OSCULES. 
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 envelops 
the stems of seaweeds, or encrusts rocks and stones; when growing on seaweeds 
it forms cake-like masses with a level surface, but when encrusting 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 
