We may always know the different species by the forms and patterns of the shells in which they live. Some have very regular shells and prettily marked. These are usually rounded or arched on one side and flat on the other.
When you are looking for various microscopic objects in pond water you will often see these tiny shells among the sediment on your slides, and if you will patiently wait a few moments you will soon see delicate, transparent arms slowly pushing out on every side like cautious feelers. (Figure 2, Amœba in Shell.—Carpenter, p. 445.)
But the most beautiful forms, and by far the greatest variety of these microscopic shells are found in the ocean and in marine deposits. If we look at the seaweeds which grow on the rocks we may see many white specks adhering to every part of the plants. With a lens we find the minute specks are spiral shells of many species belonging to the class Foraminifera, and very closely allied to the amœba. The shells are of most elegant form and pattern. The large sea-shells which we so much admire are not half so lovely in form or color as these seen through a microscope. Some of the living animals and the castles in which they dwell are crimson in color, others a delicate pink.
Let us take one of these living shells while it clings to the sea-weed and carefully cut off the smallest portion of the plant to which it adheres, so as to disturb the occupant as little as possible; and now place it in the live box with some of the salt water and we shall soon have a most beautiful sight.
See, the creature is throwing out delicate, transparent threads or filaments in every direction, like fine-spun glass. How charming it looks with the beautiful shell in the centre, surrounded by this moving, filmy halo, and how slowly and cautiously the filaments are extended! He is not a heedless, reckless creature, rushing into needless danger, but a quiet, timid citizen. Although he was such a long time throwing out his misty arms, when he scents danger he withdraws them as quick as a flash. The least jar of the live-box, or a little wriggling larva—much too large for him to manage, however—are sufficient to make him take in all of his lines; but when quiet is restored, they are again stretched out. And for what purpose are these slender filaments extended? Ah, an innocent animalcule has become entangled among the shimmering, filmy threads, and now the threads coalesce, run together like the arms of amœba, and disappear, and the animalcule is drawn within the walls of the beautiful castle, and we are left to conjecture the fate of the little victim. Figure 3, Rotalia Ornata—which shows its delicate filaments extended.
FIG. 3. ROTALIA ORNATA.
These tiny creatures have been so numerous way back in the early ages of the world, that entire strata of rocks, several feet in thickness, in various parts of the world, are made up of their skeletons. The city of Richmond, Virginia, is built over rocks, composed largely of the minute fossils of Diatomaceæ intermingled with the Foraminifera and others.
A single prepared slide of these fossils will afford entertainment for an entire evening, so great is the diversity of form and so many hundreds on one slide. The Bahama Islands furnish the finest specimens of these fossils. The slides can be procured of any large dealer in optical instruments, or, what is still better, the young microscopist can soon learn to prepare them for himself, as ample directions are given in the books on the microscope.
In bidding my young readers adieu I shall not lose entire thought of them, but often when I am engaged in looking through the microscope, I shall think and ask myself, "Are they, too, absorbed in this pleasant work, and how many will become true workers and original investigators in this great field?" We shall all know in due time, for no earnest worker in any branch of science can long remain unknown. He will be found out sooner or later. A devoted student in microscopy will become so happy over the marvellous creatures and their curious ways that he cannot keep his pleasure to himself.