These busy workers lived their little day,
and then as they died, the shell-like coverings sank to the bottom of the
sea, forming, as ages passed, thick beds of chalk, such as that of which
the white cliffs of Dover are built up.
Then, as the sounding-line searches still deeper ocean-depths, it brings up
a red clay, and this again is shown by the microscope to be composed partly
of very minute creatures of a reddish colour, which live near the surface
of the ocean, but when they die sink to the bottom.
Sponges, too, which form the home of great numbers of little radiates, grow
upon the ocean floor or near the bottom of the sea; their tiny tenants,
like minute cells, living upon still smaller creatures contained in the
water which is held by the sponge.
And we are told that in some places the bottom of the sea is strewn with
star-fishes and their relations, some of them very beautiful in form and
colour, but all formed on the same plan of a central plate, from which five
arms or fingers radiate.
Do we not better understand that the waters did indeed "swarm with swarms"
when we learn even a little about these living creatures, many of them
so small that we should not be aware of their existence if we had no
microscope to reveal to us their countless myriads?
The Mollusca form a very large group of Invertebrate animals; they live
on land as well as in the water, but the aquatic species are much more
numerous than the terrestrial, and the deep-sea dredgings are constantly
bringing to light new forms.
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