Here, again, we have a similar arrangement of teeth, row after row of which lie with their points directed towards the throat of the fish. As, however, the pike and the snake swallow their prey whole, their teeth need be nothing but points. But, as the Shark is obliged to mangle its prey, and seldom swallows it whole, its teeth are formed on a different principle, each tooth being flat, wide, sharply pointed, and having a double edge, each of which cuts like a razor. So knife-like are they, indeed, that when a whale is killed, the sharks which surround it bite off huge mouthfuls of blubber, and, as they swarm by hundreds, cause no small loss to the whalers. Many a man has lost a leg by a shark, the fish having bitten it completely through, bone and all, and there have been cases where a shark has actually severed a man’s body, going off with one half, and leaving the other clinging to the rope by which he was trying to haul himself on board. SPIKED DEFENCES. This mode of defence is, perhaps, one of the most primitive in existence, and takes a wonderful variety of forms. The spiked railings of our parks and gardens, the broken glass on walls, and even the spiked collars for dogs, are all modifications of this principle. On the illustrations are several examples of spikes used for military purposes. The first is known by the name of “Chevaux-de-frise,” and is extensively used in forming an extemporised fence where no great strength is needed. The structure is perfectly simple, consisting of a number of iron bars with sharpened ends, and an iron tube some inches in diameter, which is pierced with a double set of holes. When not in use, the bars and tube can be packed in a small compass, but when they are wanted, the bars are thrust through the holes as shown in the illustration, and the fence is completed in a few minutes. The horizontal bars are linked together by chains, so as to prevent them from being shifted, and a defence such as this is generally used for surrounding parks of artillery and the like. * * * * * ALL who have the least acquaintance with military matters must be familiar with the “Square,” and its uses in the days of old. I say in the days of old, because in the present day the rapid development of guns and rifles has entirely destroyed the old arrangement. So lately, for example, as the day of Waterloo, troops might manœuvre in safety when they were more than two hundred yards from the enemy. Now, a regiment that attempted to manœuvre in open ground would be cut to pieces by the rifles of the enemy at a thousand yards’ distance.