In the left-hand division of the illustration are shown several examples of ringed and spiral tissues belonging to the vegetable world, in which the principle is exactly the same as that of the Chinese lantern, &c. That on the right hand is an example of simple rings within a membrane. The central figure shows a double spiral, which produces very much the appearance of a series of rings; and on the extreme left is an interesting example which shows the transition in the internal supports from spirals to rings.
I have already mentioned that the proboscis of the House-fly exhibits this modification. If one of these objects be placed under a moderate power microscope—the half-inch is quite enough—and examined, it will be seen that there are some large tracheæ, just like those of the Dragon-fly larva, on each side of the proboscis, and that, where the end is widened and flattened into a sort of disc, their place is taken by a set of very much smaller tracheæ, coming nearly to a point, and each being supported internally by a series of incomplete rings, shaped very much like the letter C. A slide containing this object well mounted can be purchased at any optician’s for a shilling.
The trachea, or windpipe, as we call it, of all vertebrate animals, man included, is formed on exactly the same principle, as any one may see by going to a butcher’s shop, and looking at the trachea, or windpipe, by which the lungs, or “lights,” as they are called, are suspended. Were it not for this structure, we should not be able to bend our necks or turn our heads.
The accompanying illustration shows the tracheæ of three well-known creatures. The left-hand figure is the trachea of an Ox, the central figure that of a Pig, and the right-hand figure that of a Goose. Mr. Tuffen West, who made the drawings, sent with them the following remarks:—
“The tracheæ of animals furnish some very interesting examples of variation in the form and arrangement of the rings. Their purpose, perhaps, one can but guess at in some cases; but doubtless, as being works of the Master Builder, careful study would be repaid.
“In the Ox the rings are very strong and close, and in form like a horse-shoe with the ends approximated.
“In the Pig the incomplete rings are broad at one part, and narrow on the opposite side, with a tendency to spiral arrangement. I imagine that this would make a very rigid tube, and, indeed, it feels so in the hand.
“Then, in the Goose, the narrowed lower part is that which is figured just before the trachea reaches the sternum. The (complete) rings are twice as broad in one half as in the other, and by the alternate disposition of these differing widths, a tube is formed of great flexibility fore and aft, but almost absolutely rigid in the lateral direction. This seems to be so marked an evidence of design as to be calculated to greatly raise our admiration.”