“I have counted one hundred and thirty-six plates on one ribbon. There are two ribbons on each thoracic segment, and there are seven such segments. Hence, we may compute the total number of prehensile comb-like plates on this portion of the body to be about one thousand nine hundred, each of which is wielded by muscles at the will of the animal; while, as each plate carries on an average five teeth, there are nearly _ten thousand teeth_ hooked into the lining membrane of the cell, when the animal chooses to descend.” “Even this, however, is far short of the total number, because long ribbons of hooks of a similar structure, but of smaller dimensions, run across the abdominal segments, which are more numerous than the thoracic. No wonder, with so many muscles wielding so many grappling-hooks, that the descent is so rapidly effected.” Lastly, we come to the Walrus, whose strangely elongated upper canine teeth can be used for just the same purposes as the scaling-fork or climbing-spur. As, however, reference has already been made to these tusks, in connection with another department of this work, there is no necessity for occupying space with a second description. DEFENCE OF FORT. So much for attack; now for defence. The simplest mode of defending a fort, or even a mountain pass, is by throwing or rolling rocks and heavy stones against the enemy. Simple as it may appear, it is a very effective one, as can be well understood by those who have rolled a huge stone down a long and steep slope. The stone goes gently enough at first, but rapidly gains speed, until at last it makes great bounds from the earth, tearing and crashing through everything as if it had been shot from a cannon. I have seen a stone which was too heavy to be lifted, and had to be prised over the edge with levers, spring completely through the topmost branches of a high tree, scattering the boughs in all directions, and then, alighting on another stone, split into many fragments, just like the pieces of a burst shell. That one stone would have swept off a whole party of soldiers had they encountered it while trying to ascend the slope. This invention has also been anticipated in Nature. Putting aside the obvious reflection that the most primitive warriors must have noticed the effects of stones falling over a precipice, we have, in Captain Hall’s “Life with the Esquimaux,” a curious account of the Polar Bear and its mode of killing the Walrus. Gigantic as is this animal, and terrible as are its tusks, the Polar Bear will sometimes attack it in a very singular manner. The Bear springs on a sleeping Walrus, and clings to its shoulders with one paw, and with repeated blows from the other, fractures its skull. Still, the combat is sure to be a severe one, and so the Polar Bear will, if he can, secure his prey by some other method.