38 LIFE AND HER CHILDREN. 
take place in those cells which lie all round the 
outside of the rest ; each one of them puts forth a 
minute whip-like lash called a cilium (from cilium, 
an eyelash), so as to form a fringe round the whole 
body, and then the young sponge, being ready to 
make its own way in the world, bursts through the 
skin of the bag, and wav- 
, , 
ing its lashes, swims out 
an oval-shaped body (2, 
Fig. i i) into the sea. 
Here, you will notice, 
we have a body, not 
, made as in the simplest 
The birth of the Sponge. Adapted 
from Carter. slime-animals of a mere 
1, Sponge-egg, a, The yelk within piece of slime, but COm- 
the envelope, b. posed of a number of 
2, Young sponge swimming, c, ,, ., , 
Nipple projecting, where a large cells, the inner ones round 
hole will. afterwards form, d, Root- and without lashes, like a 
cells by which the young sponge p- rouD Q f Amoeba while 
afterwards fixes itself to the rock. & 
the outer ones, each with 
his little whip, are like a colony of monads (see Fig. 3), 
surrounding the animal. 
By means of these it swims along and feeds ; and 
as it grows, a small nipple, c, afterwards to become a 
hole, appears at the tip, while a group of larger cells (cT) 
collect at the hinder end. By means of these cells 
the little animal attaches itself to the spot where it is 
to spend the rest of its life, sometimes to a pebble, but 
generally to the solid rock. Small sponges often fix 
themselves to living shells, and Dr. Johnstone tells us 
that he met with a sponge on the back of a crab, 
which walked about quite unconcerned with its light 
burden, though it was many times larger than itself. 
