The reader may probably be acquainted with the Leaf-rolling Caterpillars, of which there are so many. I had often inspected these curled leaves, and, on comparing them with the size of the caterpillars, had noticed that the muscular strength of the insect was quite inadequate to the work which was done. That much of it was owing to the “bowsing” system, which has already been described when treating of the Toggle-joint, was very probable, but that some other force must be employed was evident. On unrolling a leaf, the hidden force was at once explained, and showed itself to be a system of accumulators exactly like those of the pistolograph or the catapult. The caterpillar spins successive belts of silken threads, and affixes them to the leaf, as shown in the illustration. These threads are nearly as elastic as the india-rubber bands of the catapult, and accordingly draw the leaf together. Another set of belts is added above the former, and, as they harden and contract in the air, they roll the leaf still further. The first row is then shortened and tightened, and a third and fourth row are added in the same fashion. So elastic are these belts, that if the leaf be carefully handled it can be almost wholly unrolled, and will spring back again as soon as the force is removed. * * * * * ANOTHER form of accumulated force may be seen in the ordinary Carriage Spring, one of which is shown in the illustration. It is made of a number of strips of elastic steel lying upon each other, and suffered to play upon each other by means of slots and rivets. The weight being placed in the centre, it is evident that this very ingenious spring is really an elastic girder, yielding to sudden pressure, and recovering itself when that pressure is removed. * * * * * INGENIOUS as is this spring, it has many parallels in Nature, one of which is here given. It is popularly thought the hoof of the horse is a solid mass of horn destined to protect the feet against hard and rough ground. Such certainly seems to be the opinion of farriers, who, in shoeing horses, act exactly as if the horn of the hoof were structureless; whereas it is a marvel of complicated mechanism. On looking at the exterior of a horse’s hoof, it will be seen to be marked with a vast number of very fine, but easily visible longitudinal lines, looking as if they were scratches from a very fine needle. If the hoof be removed from the foot, and examined upon the interior, it will be seen that each of the apparent scratches signifies the edge of a very thin plate of horn, not so thick as the paper on which this book is printed. The hoof, in fact, is built up of multitudinous plates of horn, set side by side, and each acting as a separate spring. It is this beautiful structure which allows the horse to tread without a jar being sent through its whole system by every step which it takes.