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."
[Illustration: FIG. 3.--JELLY-FISH, SHOWING TENTACLES.]
Jelly-fish vary greatly in size. Some are mere dots, so extremely small that we should not notice them in the water, while one species is said to be seven feet in diameter, with tentacles measuring fifty feet (Fig. 3). The parent of this huge jelly-fish was a hydroid only half an inch high. Its children will be the same. What do you think its grandchildren will be?
[Illustration: FIG. 4.--MUSHROOMS OF THE SEA.]
The size of jelly-fish is greatly enlarged by the water they absorb; indeed, the substance of which they are composed consists largely of water. A specimen weighing several pounds when alive will shrink away to almost nothing if exposed to the sun and the wind. As the body contains no bones or other solid matter, it all perishes together, and no trace is left of its former beautiful shape. You will see that jelly-fish are in no way like real fish. One writer found them so much like a familiar vegetable that he called them "Mushrooms of the Sea."
It would be impossible to describe to you the varied colors of jelly-fish, as they include almost every hue, the beautiful tints being probably due to their transparency. Some are purely white and as clear as glass, while all shades are to be found, from pale blue and pink, to bright red and yellow. Those found in tropical seas are of a deeper color than ours.
In striking contrast with these brilliant jelly-fish is one species which is so delicate and transparent that as it floats upon the water we can scarcely see the substance of which it is composed. The only parts that strike the eye are the circular tube around the edge and the four radiating tubes with their large clusters of eggs. The tubes look as if they were held together by some slight web. The movements of this jelly-fish are languid, and it sometimes remains perfectly quiet in the bright sunshine for hours, not even moving its tentacles.