the type of the paddles of the Ichthyosaurus and Plesiosaurus.
Extending a similar comparison through the four great classes of vertebral animals, we find in each species a varied adaptation of analogous parts, to the different circumstances and conditions in which it was intended to be placed. Ascending from the lower orders, we trace a gradual advancement in structure and office, till we arrive at those whose functions are the most exalted: thus, the tin of the fish becomes the paddle of the reptile Plesiosaurus and Ichthyosaurus; the same organ is converted into the wing of the Pterodactyle, the bird and bat; it becomes the fore-foot, or paw, in quadrupeds that move upon the land, and attains its highest consummation in the arm and hand of rational man.
I will conclude these observations in the words and with the feelings of Mr. Conybeare, which must be in unison with those of all who had the pleasure to follow him through his masterly investigations of this curious subject, from which great part of our information respecting the genus Plesiosaurus has been derived:
"To the observer actually engaged in tracing the various links that bind together the chain of organized beings, and struck at every instant by the development of the most beautiful analogies, almost every detail of comparative anatomy, however minute, acquires an interest, and even a charm; since he is continually presented with fresh proof of the great general law, which Scarpa himself; one of its most able investigators, has so elegantly expressed: 'Usque adeo natura, una eadem semper atque multiplex, disparibus etiam formis effectus pares, admirabili quadam varietatum simplicitate conciliate.'"
