On the extreme right is a corresponding spiral cell from the common Lily, in which the spring power is given by two fibres twisted in opposite directions. The reader will now understand and admire the mechanism by which these plants attain their great strength and elasticity, the stems being made of myriads of these spiral fibres. The oval body on the upper part of the illustration is a poison-cell of a marine polyp, and is given here as an example of an animal spiral spring, the others all belonging to the vegetable world. We shall see more of its structure a little further on, and will not now examine it in detail. The two remaining figures represent the remarkable objects called Antherozoids, _i.e._ the living creatures of anthers. They exist in vast numbers in the non-flowering plants, and inhabit those parts which correspond with the anthers of the flowering plants. When placed in water they have a curious way of coiling and twisting themselves spirally, so as to make their way through the water in a tortuous, but tolerably rapid, course. This movement is effected by the contraction and expansion of the spirally twisted filament. The upper figure represents a group of Antherozoids in their cells, and the lower is a much more magnified figure of a single Antherozoid as it appears when free, and in the act of moving through the water. * * * * * ON the accompanying illustration are many examples of Spiral Springs, both natural and artificial. We will take these in their order. The upper left-hand figure represents the “Buffer,” by which the carriages of railway trains are prevented from jarring against each other. Perhaps some of my readers may be old enough to remember the days of the old railway carriages that were connected by short chains, and furnished with buffers that were merely padded. As the train started a separate jerk was given to every carriage by the tightening of the chains, and, as it stopped, all the carriages bumped against each other in a most unpleasant manner. Now, however, the buffers are furnished with powerful springs, and are pressed strongly against each other by means of screw-bolts, so that they form one continuous line. In fact--and here is another analogy between Art and Nature--a train, when properly made up, bears a close resemblance to a human spine, the carriages being analogous to the vertebræ, and the spring buffers to the elastic cartilages between the vertebræ.