HO W SPONGES LIVE. 49 
the strength to tear it away ; and these, needing no 
further protection, are made entirely of soft fibre. 
Here we must leave the history of sponges and 
their lives. We have left much unsaid, for to tell 
how sponges may increase by dividing or by budding, 
as well as by eggs, would have taken us too far into 
detail ; neither could we give space to trace the 
wonderful way in which the various spicules are used 
as weapons of defence ; and for special examples of 
the different kinds of sponges you must consult works 
on natural history. We have had one chief object in 
view, namely, to see how Life in this new form has 
advanced beyond the earliest slime -animals. The 
sponge, with its two forms of cells and its division of 
labour, stands already far above the microscopic 
beings of our last chapter. Rooted to the rocks, and 
large enough to invite the attacks of enemies, it has 
yet learnt to protect itself by wonderful structures, 
to distribute its food throughout a large body, and 
last, but not least, no longer to form its skeleton 
merely of flint or lime, but to manufacture in its own 
body the material with which it builds. 
It has indeed succeeded so well that Dr. Bower- 
bank, one of the best authorities on sponge life, came 
to the conclusion that sponges are able to escape 
almost entirely, during their lifetime, from becoming 
the food of other animals. It is only after their 
death that their slime serves to nourish myriads of 
minute creatures, and then the wonderful rapidity 
with which the living matter is devoured, is quite 
enough to prove to us how well the living sponge 
must have used its weapons to protect itself, while 
still it was one of Life's living children. 
