THE BREAD-CRUMB SPONGE 133 



times greenish in colour and sometimes yellow, 

 which grows round the stems of sea-weed, or 

 covers the surfaces of rocks and stones. And 

 the odd thing about it is that when it clings to 

 sea-weeds its surface is quite smooth, with a 

 number of large holes in it, but that when it 

 grows on rocks it is covered all over with little 

 projections which look just like the craters of 

 volcanoes. 



It is rather difficult to describe the animal 

 which lives in the sponge, for it really consists 

 of a large number of tiny animals all joined 

 together in one common mass, very much like 

 the polyps of the sea finger. But they are so 

 very small that unless you examine them by 

 means of a good strong microscope they only 

 look like a mass of brownish jelly. 



These little creatures obtain their food in a 

 very curious way. If you look at the surface 

 of the sponge through a magnifying glass, you 

 will see that it is pierced by a great many very 

 tiny holes as well as by a number of bigger 

 ones. Now water is always passing in through 

 the small holes and out again through the big 

 ones; and as it does so the little creatures 

 manage to suck out all the tiny atoms of animal 

 and vegetable matter which were floating about 

 in it. 



