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. Some of the shells which protect their soft bodies, and are formed by the animals themselves, are marvels of beauty, and many of them are secured from injury by a waterproof coating. A number of extinct animals, such as Ammonites and Belemnites, belong to this group—their shells may be seen in any good museum; those of the Belemnites, as their name implies, are shaped like a dart; those of the Ammonites, like that of the beautiful Nautilus of our times; but the fisherfolk of Whitby, where they are found in numbers, say they are "snakes turned to stone."
But as we have been speaking so much of sea-creatures, I think we will now leave the oysters, cockles, mussels, and razor-fish, and choose the familiar garden-snail as our specimen of the Mollusca, or Soft-bodied Family. I fancy you need no introduction to that snug little householder. Often, however, as you have touched his soft horns, you possibly do not know that the very house in which you first made his acquaintance has been his habitation ever since; for young snails come from the egg with the shell upon their backs, and they never quit that first house for a larger one, for as they grow, their shell-house grows too. Look at this empty snail shell, and say whether God has not given a beautiful coat of mail to protect a creature without a bone in its body, and so sensitive that
"Give but his horns the slightest touch,
His self-collecting power is such,
He shrinks into his house, with much
Displeasure."
But how does the house grow large so as to suit the growing tenant? Most shells are made from a part of the animal called the mantle, and increase round the rim; if the snail's house is broken, its slime will harden over the injured part and repair it. Then, when the cold weather comes, and the snail prepares to bury itself underground for several months, and take its winter nap, it makes a strong cement of earth and slime, with which it builds up the open part of its shell—but, wonderful to think of, the clever little mason leaves, as it were, one brick out of the wall, and thus there is a tiny opening, too small to let in the water, but large enough to admit air sufficient to keep him alive during his long sleep.
Now that our snail has been good enough to put out those four horns of his, let us ask what purpose they serve, and why they are placed' where they are. The answer is very simple; these "feelers" are to the snail instead of arms and legs; and the upper pair have eyes at the end, so that the wary little traveller, as it drags itself along a broad cabbage leaf, leaving a slimy track behind it, can tell, both by sight and touch, what obstacles may lie in its path. I don't know whether you have ever seen the eggs of snails; I have not, but I have heard that they are about the size of peas, and are buried in the earth, as the crocodile's eggs are buried in the sand.
Of the many families of Ringed or Jointed Animals, we will choose the Crabs and Lobsters first. They are encased in armour of shell, and this has given to them and their relations the name of Crustaceans, or Crusty creatures, because what bones they have are outside, not hidden beneath the flesh. But unlike the snail's house, which grows with the growth of its inmate, and unlike our skeleton which grows as we grow, this close-fitting armour does not increase in size, nor is it elastic enough to expand, but every year one coat of mail is cast off, in a way not unlike the sloughing of the serpent, to make room for a fresh soft suit. This new suit soon hardens, and the creatures embrace the opportunity to make a little progress in growing, which they do by fits and starts, not continuously; for the shell, when once hardened, gives them no room to increase in size—they have to wait till next year! The long pointed claws of the crab and lobster are easily broken, and sometimes lost altogether, so that the power which they have of growing new ones is a wonderful provision for their life among the rough rocks and tangled sea-weeds.