38 
LIFE AND HER CHILDREN. 
Fig. ii 
« 
m 
2 
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 a/mm, 
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. 1 1) into the sea. 
Here, you will notice, 
we have a body, not 
made as in the simplest 
slime-animals of a mere 
piece of slime, but com- 
posed of a number of 
cells, the inner ones round 
and without lashes, like a 
group of Amoeba, while 
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 y afterwards to become a 
hole, appears at the tip, while a group of larger cells (d) 
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. 
The birth of the Sponge. — Adapted 
from Carter, 
1, Sponge-egg. #, The yelk within 
the envelope, b. 
2, Young sponge swimming, c, 
Nipple projecting, where a large 
hole will. afterwards form, d, Root- 
cells by which the young sponge 
afterwards fixes itself to the rock. 
