Upon the outer edge of the bell there are bright-colored specks and solid spots, which are thought to be the beginnings of eyes and ears. Although they never grow to be perfect eyes and ears in the jelly-fish, they promise that Nature has in store for her children the precious gifts of sight and hearing. Such imperfect organs are called by the wise men rudimentary organs. This is the lowest animal in which anything corresponding to our nerves is found.
Fig. 2.—Lasso Cells from a Fresh-water Hydroid (Magnified).
Delicate fringes and tentacles hang from the lower edge of the bell, adding greatly to its beauty. The tentacles are often many feet long, yet the animal has the power of drawing them up so that they are not visible. This curious power of contracting and expanding the tentacles belongs to many humble sea creatures, and you will be greatly interested in watching their movements. Sometimes, while we are still wondering at their disappearance, they lengthen again as if by magic.
The tentacles of jelly-fish are covered with a great many lasso cells. These lasso cells are too small to be seen without a microscope; still, they are powerful weapons in their way, and are quite sufficient to enable the jelly-fish to catch its food. Many of you know how the skillful hunter uses a lasso for catching wild cattle. The jelly-fish uses its lasso in quite a different manner, but it may be equally unfailing.
When examined, each lasso cell, or little sac, is found to contain a long slender thread, coiled within it, somewhat like a lasso, and floating in a fluid. The cell is filled so full of the fluid that it bursts with the slightest touch, and as the fluid squirts out, it carries with it the slender lasso armed with sharp stings. In this way lassoes are darted out to capture many little crabs or fish that brush too near in passing.
Fig. 3.—Jelly-Fish, showing Tentacles.
The sting of the lasso seems to paralyze the unfortunate creatures, and they make no effort to escape as the tentacles coil round them and carry them to the mouth of the greedy jelly-fish. In Fig. 2 you will see a group of lasso cells highly magnified. The cell at a has not yet burst, and through its thin walls we see the barbed dart at the end of the lasso. At b the lasso has been thrown out only a short distance, while at c the long slender lasso still carries the dart at the end, and the curious little bladder is much larger than it was inside the cell. The lasso cells of this specimen are exceedingly delicate and simple, but in some animals the lasso may be seen coiled within the cell; and when thrust out it bristles with sharp stings. Is it not a dainty weapon to be used in the continual warfare carried on by these innocent-looking creatures? Small as the lasso cells are, they serve to protect the soft-bodied animals from their numerous enemies.
Jelly-fish would hot hesitate in the least to use these tiny weapons upon us if we should touch their soft, pretty tentacles with too much familiarity. The irritation produced in the flesh by the numerous sharp points on the lassoes is similar to the stinging of nettles. For this reason jelly-fish are often called sea-nettles. The correct name, however, which you will find in scientific books, is "Medusæ."