DISTRIBUTION OF ORGANISMS. 201 



than a seal, while the anterior extremities short, and in some 

 instances, scaled, rather than feathered do not serve for flight, 

 but are used exactly like the paddles of the marine turtles in 

 propelling the body through the water : often for several 

 hundred yards under it. There is some reason for believing 

 that the Birds are derived solely from one order of the Rep- 

 tiles, and that this is the cause of their more concentrated 

 unity of structure. The affinity to that inferior class is cer- 

 tainly less clearly shown than are the affinities which pervade 

 the class itself ; but it may be asked if we can be sure that 

 the transition from class to class was always to give interme- 

 diate forms, or that these, if given, were necessarily to be pre- 

 served, either as living suecies or as fossils 1 The Chelonia 



o Jr 



present a sufficient variety of characters to have been the sole 

 parentage of the Bird class ; many being fierce and carnivo- 

 rous, while others are vegetable feeders and of gentle character. 

 They are now chiefly tropical, while the swimming birds 

 are hyperboreal ; but the secondary and tertiary formations 

 show that the chelonia were once much more widely distributed 

 than they now are. 



The first of the great stirpes is that which gives us the birds 

 most important of all to us the domestic poultry. Its root 

 appears in certain of the natatorial families, the Divers 

 (Colyinbidce), Grebes, etc. These are Swimmers native to the 

 Arctic Ocean, though accustomed to migrate southward in 

 winter. They are immediately followed by the Mergansers, 

 Ducks, Geese, Swans, (Anatidce,) and the Phalleropes (Phalle- 

 ro'pidce), Gallinules, and Coots (Lobipedidtf), which still pre- 

 serve the aquatic habits, and the webbed or lobated feet 

 necessary for progression in the water, but tend more to 

 residence in rivers and other inland waters. In these, how- 

 ever, we see a clear separation into three subdivisions, one 

 composed of the Mergansers and Ducks, which live in great 

 part upon animal matters, another comprising the Geese and 

 Swans, which are purely vegetable feeders, and a third em- 

 bracing the Gallinules and Coots, whose diet is mixed. 



The hypothetic history of these animals is so distinct, that 

 it might almost be set down as a series of recorded events. 

 Their tendency, in consequence of tastes in aliment, was to 

 advance along rivers and the shores of lakes, to those adjacent 

 low grounds where vegetable food, worms, and insects are to 

 be found. They landed, we may say, either upon sandy 

 beaches, or upon those low shores which, in the early ages of 



