HOW SPONGES LIVE. 
37 
Fig. 10. 
gine that we can visit one of the sponge -colonies 
in the Mediterranean Sea 
or the Gulf of Mexico, 
where the rocks from fifty 
to a hundred and fifty feet 
below the surface of the 
clear blue water are covered 
with sponges of every size, 
and shape, and texture. 
If we could visit these 
sponge - beds during the 
summer or autumn months, 
and examine carefully the 
slimy lining of one of the 
big tubes of a living 
sponge, we should find that 
minute bags of slime 
(i, a, Fig. 1 1) are begin- 
ning to appear in it, either 
scattered through the 
sponge or collected in heaps. 
These are sponge-eggs, out 
of which young sponges 
are to grow, and in many 
ways they are very like a hen's egg. Within, 
as may be seen through their transparent cover- 
ing, is something which answers to the yelk of 
an egg, with a solid spot or nucleus in it. This 
yelk begins soon to divide into two cells, or separate 
masses of slime, and these again divide into four, 
these four into eight, and so on till the egg is a 
globe of small round cells, the beginning of the 
young sponge. And now a change may be seen to 
A British sponge found at 
Brighton life-size. 
