166 MARINE SAURIANS. 



nise the type of the paddles of the Ichthyosaurus and Ple- 

 siosaurus. 



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 cir- 

 cumstances 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 

 fin 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. 



1 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 conciliat.' " 



