The upper figure represents the jaws of a Pike, with their terrible array of reverted teeth. The Pike, as every one knows, feeds upon other fish, and eats them in a curious manner. It darts at them furiously, and generally catches them in the middle of the body. After holding them for a time, for the purpose, as I imagine, of disabling them, it loosens its hold, makes another snap, seizes the fish by the head, and swallows it. The Pike is so voracious that it will attack and eat fish not very much smaller than itself, for its digestion is so rapid that the head and shoulders of a swallowed fish have been found to be half digested, while the tail was sticking out of the Pike’s mouth. Unless, therefore, the teeth of the Pike were so formed as to resist any retrograde movement on the part of the prey, the fish would starve; for, lank and lean as it is, the Pike is one of the most voracious creatures in existence, never seeming able to get enough to eat, and yet, as is often found in such cases, capable of sustaining a lengthened fast. How well adapted is this arrangement of teeth for preventing the escape of prey, any one can tell who, in his early days of angling, caught a Pike, and, after killing it, tried to extract the hook without previously propping the jaws open. If once the hand be inserted between the jaws, to get it out again is almost impossible without assistance, and often has the spectacle been exhibited of a youthful angler returning disconsolately home, with his right hand in the mouth of a Pike, and supporting the weight of the fish with his left. * * * * * THE teeth of a serpent are set in a similar manner, as can be seen by reference to the illustration on page 80. An admirable example of the power of this arrangement may be seen in the jaws of our common Grass or Ringed Snake (_Coluber natrix_). The teeth are quite small, very short, and not thicker than fine needle-points. Yet, when once the snake has seized one of the hind-feet of a frog, all efforts to escape on the part of the latter are useless. The lower jaw is pushed forward, and then retracted, and at each movement the leg is drawn further into the snake’s mouth, until it reaches the junction. The snake then waits quietly until the frog tries to free itself by pushing with its other foot against the snake’s mouth. That foot is then seized, the leg gradually following its companion, and in this way the whole frog is drawn into the interior of the snake. I have seen many frogs thus eaten, but never knew one to escape after it had been once seized by the snake. As these reptiles are perfectly harmless, it is easy to try the experiment by putting the finger into a snake’s mouth, when it will be found that the assistance of the other hand will be needful in order to extricate it. * * * * * BELOW the head of the pike is a view of a Shark’s jaws, as seen from the front.