Part 33

We will not read farther to-day, as I want to tell you in this chapter something about life in what are called its lower forms, and we shall find that wherever we may look, every creature is perfect in itself, and perfectly suited to the life appointed to it by its Creator, and the home where He has placed it.

My children had learnt something about the two great divisions of animals, those which belong to the great Backboned Family and those which have no backbone. It is of the latter that we shall speak today. You know that a fish has a backbone, and that it is beautifully formed, for you have often seen it; but perhaps you have not noticed that a lobster, though called one of the shell-fish, is quite unlike the true Fishes: its skeleton is not inside, but outside; there are no bones within, but all the soft parts are inside, and the hard parts outside; while the body of a fish is formed on just the opposite plan. The fish is called a Vertebrate animal, because it has a backbone, made up of numbers of separate bones called vertebras. Some of us know that this word comes from the Latin, and means that which turns, because these many small bones are so beautifully jointed together as to be all perfectly moveable, so that the long bone which they form is very flexible. Some snakes have more than three hundred of these vertebræ, and you know how they can coil and twist their glittering length.

The marks of a Vertebrate animal are very easy to remember.

It must have this wonderfully jointed backbone, and also what is called the skeleton, which is a framework of bone.

A spinal cord (from which this division of animals is sometimes called the "Chordate").

Four limbs, and red blood.

In these respects all the animals which belong to this division are alike, though in general appearance they may be as unlike each other as a horse is unlike a bird, or a crocodile unlike a herring.

Few things in nature are more wonderful than the way in which this Vertebrate plan has been fitted to animals differing from each other in all other respects.

Now let us look at the marks of an Invertebrate or Inchordate animal.

It has no backbone, and instead of a bony framework within, to support the soft parts of its body, it generally has a hard shell, or thickened skin outside, to protect the softer inner parts.

It has no red blood.

Now, just as plants have been arranged in different classes, so animals are classified according to the various plans upon which they have been formed. So, besides the two great divisions of the Vertebrates and the Invertebrates, the latter have been classed as--

(a) Radiata, or Rayed Animals--those whose parts all radiate from a common centre--such as the starfish, red-coral, sea-anemone.

(b) Mollusca, or Soft-bodied Animals, protected by shells--such as snails, oysters, limpets. (The members of this family are numerous indeed).

(c) Annulosa, or Ringed Animals--those whose bodies are composed of many parts, jointed together--such as crabs, spiders, bees, ants, centipedes, shrimps, and many more; for this great family has relations among all the insect tribes.

It is very beautiful to see that God has formed His creatures on such different plans, and though we shall be able to say very little about them, I hope you will by-and-by study Natural History, and learn more and more of His care in fitting each for the life it has to live. But remember that all these types of animals, the Radiates, Molluscs, Articulates (as the members of the "ringed" family are sometimes sailed), existed in the most ancient times: they lived side by side, as it were, and were not, as some philosophers would have us believe, derived from each other. Each was "after its kind," and each species remains; animals may alter from changes in their way of life, but there is no passing from one kind to another.

Now I think you will be interested to hear that in the Stone Book, some of the most ancient "letters" are formed from creatures belonging to the Invertebrate Group. We were speaking just now of the white clay brought up from the depths of the Atlantic Ocean by the sounding line. The microscope shows that it consists of the imperishable part of creatures, tinier than any you can imagine, which had the power when living of extracting from the sea-water--as I told you is the way of the corals--the lime which formed their outer coat, or skeleton. 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. 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.

One of the crusty creatures you know well enough, and you can find it without going to the seaside, I mean the wood-louse, which I used to hear called a "carpenter" when I was a child. In damp places, you can hardly turn over a mossy stone, or pick off a bit of bark from a fallen tree, without disturbing a whole colony of these slate-coloured creatures, with their mailed coats, made of ten rings, or plates of armour. They seem to know the use of their armour well enough, for if disturbed you will see them either scurry off as fast as their many little feet can carry them--and they are able to run forward or backward at pleasure--or else roll themselves up into tight balls, so that feet and head and feelers are all safe, under the ringed shield which God has given them as a defence and protection.