oldest animals, the effectiveness of the youthful structure. We may now understand how the mosasaurs seized and swallowed their prey. Living constantly in the water, away from all firm objects, with small, short limbs quite incapable of holding struggling prey, and the body not sufficiently serpentine to hold it in its folds after the manner of snakes, the mosasaurs would have found it difficult or impossible to swallow fishes of even moderate size, were their jaws of the same construction as are those of the land lizards. If they preyed upon small animals only, or if they tore their prey to pieces after the manner of the alligators, there would have been no especial difficulty in deglutition. But it is certain that the animals which the mosasaurs devoured were not always small, and they must have been swallowed whole, since their teeth were not adapted, like those of the alligators and true crocodiles, for the rending of bodies. One who has watched a snake swallow a frog or another snake will appreciate the difficulties against which the mosasaurs contended in swallowing fishes a fifth or a sixth of the length of their own bodies. The ordinary snake, no matter where or how it seizes its prey, invariably swallows it head first. Its mandibles are even more loosely united in front than were those of the mosasaurs, and while there is no joint in the snake’s mandibles such as there is in the mosasaurs’, the loose union of the various bones of the mandibles serves the same purpose. The frog or lizard, while firmly held by the slender teeth, is slowly moved sideways by the alternate lateral action of the jaws till the head is reached. Many non-poisonous snakes, if they find it impracticable or impossible to reverse the position of their prey in this way, wrap the folds of their body about it, holding it firmly while they release their mouth-hold and seize it by the head. An amusing instance of these habits came under the observation of the writer not long ago, in Texas. A large “blue racer” (_Bascanion_), six feet four inches in length, caught an unusually large bullfrog by one hind leg, but in almost less time than it takes to relate, the head of the frog had entered the snake’s gullet and the mouth was closed over it, notwithstanding the vigorous muscular and vocal protests on the part of the frog. Wishing to secure the skull of the snake for his collection, the writer seized an ax standing conveniently by and cut the snake cleanly in two. The peristaltic action of the deglutitional muscles carried the frog slowly on about two feet farther to the ax-made orifice, from which it emerged, and, after a few croakings against such unkind usage, calmly hopped off into the near-by pool of water! Many poisonous snakes release their prey after killing it; other snakes may force their prey down the throat by pressing it against the ground.