Telescopic Tubes, their Structure and Uses.—The Japanese Fishing-rod.—The Tripod Wheel-bearer and its Telescopic Structure.—The Rat-tailed Maggot.—Locomotion.—Direct Action.—The Rocket, the Water Tourniquet, and Electric Tourniquet.—Cuttle-fish.—The Flying Squids.—The Paper Nautilus.—Proceedings of newly-hatched Calamaries.—Larva of the Dragonfly.—Distribution of Weight.—The Snow-shoe, its Structure and Mode of using it.—The Skidor of Norway.—A formidable Rifle Corps.—The Mud-patten.—Foot of Duck tribe.—Foot of Jacana.—Locomotion of Water-gnat.—Tree-climbing.—Mode of ascending Palm-trees.—The Value of a Hoop.—The “Girt Pupa” and Butterfly.—Principle of the Wheel.—The primitive Wooden Wheel.—Spoked Wheels.—Driving Wheel of the Bicycle.—Naturally spoked Wheel of the Chirodota.
Means and Appliances (continued).
WE will now treat rather more in detail the two subjects which were lightly touched upon at the end of the last chapter.
The reader will remember that the diamond-headed borer is made in telescope form, so as to be adjustable at pleasure. It was also remarked that the ovipositor of the Gad-fly was made in a similar fashion, so as to be withdrawn within the body of the insect when not needed, and protrusible to a considerable extent when the Gad-fly wishes to deposit her eggs.
As to our modern telescopes and opera-glasses, they are so familiar that there is little use in describing them, except to say that their framework consists of a number of tubes of gradually lessening diameter, the one sliding within the other, so that the instrument can be lengthened or shortened at will, so as to suit the focus of the observing eye.
A very ingenious adaptation of the telescopic principle is seen in the Japanese fishing-rod, which is now tolerably well known. Our own telescopic rods require to be withdrawn at the butt-end, and then fitted together in front. But the Japanese rods are so made that, after taking off the ferrule of the seeming walking-stick, a mere fling of the hand will send joint after joint flying out, and fixing themselves in regular succession. So admirably are these rods made, that even blowing into the butt-end will have the same effect.
One of the most perfect, if not the most perfect, example of the telescopic tube is to be found in the Tripod Wheel-bearer (Actinurus), one of the numerous aquatic Rotifers.
It is not usually so small as the generality of its class, being nearly one-twentieth of an inch in length, and visible to the unassisted eye, provided that the owner of the eye in question knows how to use it.
When placed under a microscope of moderate power, the Actinurus is seen to be built almost wholly upon the telescopic pattern. Only the centre of the body remains stationary, the two ends being framed on the principle of the telescopic tube, and capable of being enclosed within the central portion, just as is the case with the Japanese fishing-rod.