When the mud has quite subsided, and the water become clear, the long slender tails of the larvæ will be seen so elongated that their tips reach just above the surface of the water. A magnifying-glass will easily show the two tubes within the tail.
Let the glass be but slightly tapped, and all the tail is withdrawn in a moment, so as to be out of reach of external danger. The magnifying-glass will then show the two tubes lying contracted in the base of the tail, and taking astonishingly little space, considering the amount of elongation which they can sustain. And, on examining the various bends and curves of the tubes, the value and power of the spiral spring will at once be seen. True, they are very small, but in Nature all things go by comparison, and our whole earth itself is as a grain of sand upon the seashore among the grandeurs of the visible universe.
The Leaping Spring.
The last of the springs which can be mentioned in this work are those which are used for leaping purposes.
The figure on the right hand represents the common Spring-jack or Skip-jack with which children are always so much amused. It consists of a flattened piece of wood called the “tongue,” which is inserted into a twisted string, so that it forms a tolerably powerful spring. When twisted round, and then suddenly released, it strikes against the ground with such force that the whole machine is thrown into the air.
Sometimes the Skip-jack is made of a fowl’s merrythought, as shown in the illustration; sometimes of the breast-bone of a goose; and sometimes of a piece of wood cut into the semblance of a frog, and painted. In all cases, however, the machinery is practically the same. I may mention en passant that these frog Skip-jacks are most acceptable presents to savage chiefs in many parts of the world, and that the most powerful and venerable warriors are as delighted with these toys as any European child of six years old.
Now we will turn to Nature, and see what she has in the way of Skip-jacks.
All entomologists will at once have before their minds the vast groups of Skip-jack Beetles, technically termed Elateridæ, and also known as Click-beetles, from the sharp clicking sound which they produce when in the execution of their curious gymnastics. To this group belong the fire-flies of warm countries, and it may be mentioned that the larvæ of some of our species are too familiar to the agriculturist under the name “wireworm.”
All these beetles have very short legs and very long bodies, so that if they should fall on their backs on a smooth surface, they could not recover themselves. Now, as they, when discovered, instinctively try to save themselves by falling to the ground, it is evident that some means must be used to enable them to regain their position. This is found in a most curious apparatus.