Young Folks' Library, Volume XI (of 20) / Wonders of Earth, Sea and Sky

by Unknown

Now, though the plants themselves die, or become the food of minute animals, the flinty skeletons are not destroyed, but go on accumulating in the waters of the ponds, lakes, rivers, and seas, all over the world. Untold millions have no doubt crumbled to dust and gone back into the waters, but untold millions also have survived. The towns of Berlin in Europe and of Richmond in the United States are actually built upon ground called "infusorial earth," composed almost entirely of valves of these minute diatoms which have accumulated to a thickness of more than eighty feet! Those under Berlin are fresh-water forms, and must have lived in a lake, while those of Richmond belong to salt-water forms. Every inch of the ground under those cities represents thousands and thousands of living plants which flourished in ages long gone by, and were no larger than those you will see presently under the microscope.

These are a very few of the microscopic inhabitants of my pond, but, as you will confuse them if I show you too many, we will conclude with two rather larger specimens, and examine them carefully. The first, called the Cydippe, is a lovely, transparent living ball, which I want to explain to you because it is so wondrously beautiful. The second, the Sea-mat or Flustra, looks like a crumpled drab-colored seaweed, but is really composed of many thousands of grottos, the homes of tiny sea-animals.

1, Animal with tentacles t, bearing small tendrils t'. 2, Body of animal enlarged. m, Mouth. c, Digestive cavity. s, Sac into which the tentacles are withdrawn. p, Bands with comb-like plates. 3, Portion of a band enlarged to show the moving plates p.

Let us take the Cydippe first (1, Fig. 9). I have six here, each in a separate tumbler, and could have brought many more, for when I dipped my net in the pool yesterday such numbers were caught in it that I believe the retreating tide must just have left a shoal behind. Put a tumbler on the desk in front of you, and if the light falls well upon it you will see a transparent ball about the size of a large pea marked with eight bright bands, which begin at the lower end of the ball and reach nearly to the top, dividing the outside into sections like the ribs of a melon. The creature is so perfectly transparent that you can count all the eight bands.

At the top of the ball is a slight bulge which is the mouth (m 2, Fig. 9), and from it, inside the ball hangs a long bag or stomach, which opens below into a cavity, from which two canals branch out, one on each side, and these divide again into four canals which go one into each of the tubes running down the bands. From this cavity the food, which is digested in the stomach, is carried by the canals all over the body. The smaller tubes which branch out of these canals cannot be seen clearly without a very strong lens, and the only other parts you can discern in this transparent ball are two long sacs on each side of the lower end. These are the tentacle sacs, in which are coiled up the tentacles, which we shall describe presently. Lastly you can notice that the bands outside the globe are broader in the middle than at the ends, and are striped across by a number of ridges.

In moving the tumblers the water has naturally been shaken, and the creature being alarmed will probably at first remain motionless. But very soon it will begin to play in the water, rising and falling, and swimming gracefully from side to side. Now you will notice a curious effect, for the bands will glitter and become tinged with prismatic colors, till, as it moves more and more rapidly these colors, reflected in the jelly, seem to tinge the whole ball with colors like those on a soap-bubble, while from the two sacs below come forth two long transparent threads like spun glass. At first these appear to be simple threads, but as they gradually open out to about four or five inches, smaller threads uncoil on each side of the line till there are about fifty on each line. These short tendrils are never still for long; as the main threads wave to and fro, some of the shorter ones coil up and hang like tiny beads, then these uncoil and others roll up, so that these graceful floating lines are never two seconds alike.

We do not really know their use. Sometimes the creature anchors itself by them, rising and falling as they stretch out or coil up; but more often they float idly behind it in the water. At first you would perhaps think that they served to drive the ball through the water, but this is done by a special apparatus. The cross ridges which we noticed on the bands are really flat comb-like plates (p, Fig. 9), of which there are about twenty or thirty on each band; and these vibrate very rapidly, so that two hundred or more paddles drive the tiny ball through the water. This is the cause of the prismatic colors; for iridescent tints are produced by the play of light upon the glittering plates, as they incessantly change their angle. Sometimes they move all at once, sometimes only a few at a time, and it is evident the creature controls them at will.

This lovely fairy-like globe, with its long floating tentacles and rainbow tints, was for a long time classed with the jelly-fish; but it really is most nearly related to the sea-anemones, as it has a true central cavity which acts as a stomach, and many other points in common with the Actinozoa. We cannot help wondering, as the little being glides hither and thither, whether it can see where it is going. It has nerves of a low kind which start from a little dark spot (ng) exactly at the south pole of the ball, and at that point a sense-organ of some kind exists, but what impression the creature gains from it of the world outside we cannot tell.

I am afraid you may think it dull to turn from such a beautiful being as this, to the gray leaf which looks only like a dead dry seaweed; yet you will be wrong, for a more wonderful history attaches to this crumpled dead-looking leaf than to the lovely jelly-globe.