HOW SPONGES LIVE. 
anchored to the bottom by long flint tl ■ 
several feet long, looking like the fin< I pun gl< 
And now we find the , 
sponge-animal advancin g 
yet a Step farther, and 
beginning no longer to 
build entirely with lime 
and flint taken from the 
water, but to manufacture 
its own material. We all 
know that the spider spins 
its web of threads of 
gum formed in its body, 
and that the silk of the 
silkworm is made in the 
same manner, and now we 
have to learn that the 
sponge - animal with its 
simple! slime cells can do 
this too! For all the 
sponges which we use are 
made of fine fibres, which 
prove, when examined, to 
differverylittle chemically 
from the silk ^f the silk- 
worm. These fibres ha\ e 
been secreted by the slime- 
animal out o\ its food, and 
by en tssing and re en >ss- 
ing them in all direct i* >ns 
it tonus the soft elastic 
skelett mi * 't the toilet S] l 
carelessly or without purpose, foi we ha\ 
* J 
\ 
