264 ON THE CLASSES OF THE 



in those particular parts of the structure where the gene- 

 ral affinity is visible, no two animals can differ so much 

 from each other as a bird and a tortoise. The active te- 

 nant of the air and the proverbially sluggish reptile seem, 

 at first sight, to have no quality in common, and indeed, 

 though their connexion is indicated by every zoologist who 

 has written on the subject, there is a broad line of di- 

 stinction to be drawn between them. We require, for 

 instance, to see some animals of an intermediate construc- 

 tion ; and as none such are known, the advocates for abso- 

 lute divisions will at once conclude that they are not to 

 be found. The safer method, however, would be to con- 

 tent ourselves with the undoubted fact that they have not 

 yet been discovered. Nevertheless, by examining a com- 

 mon turtle, we may obtain the knowledge of some curious 

 points of natural arrangement. Thus we conclude in the 

 first place, that the birds which come the nearest to this 

 animal in structure must be aquatic; that they ought to 

 be covered with scales rather than with plumes; that 

 their, sternum ought to be very large, protecting all their 

 viscera ; their wings short, of no use for flight, but serving 

 rather as fins to swim with ; finally, that their legs ought 

 to be placed so far behind as to render the bird almost in- 

 capable of walking. They ought in short to be true rep- 

 tiles with respect to locomotion. If such then be the sort 

 of bird we are to look for, who does not see the Patagonian 

 Penguin or the genus Aptenodytes of Forster in the above 

 description? a bird whose olfactory organs are almost as 

 simple as those of the Chelonians, which, hke a turtle 

 dragging itself on its belly along the shores of South Ame- 

 rica, quits the sea only for the purpose of depositing its 

 eggs in the sand. 



