413 ' ROSS ON EVOLUTION. 



are representative of those which the group to which it belongs has 

 undergone. In other respects /. Dispar had well marked Reptilian 

 and even Ichthic characteristics, i^n other words was of a very 

 synthetic type. The Archmo'pteryx macrurus of the Jurassic 

 Period had, in accordance with the same law, still more marked 

 Keptilian characteristics.* 



Of all Vertebrates the Sub-class Amphibia is the most obviously 

 suggestive and instructive in the metamorphoses w^hich it undergoes 

 after leaving the Qgg, shewing, in the common Frog, for example, 

 how a creature approximating to the typical organization of the 

 earlier Fishes, living only in the water, breathing by means of gills, 

 subsisting chiefly on vegetable food, without limbs but with a 

 muscular system adapted to use the tail in swimming as the sole 

 means of locomotion, develops into an Amphibian without a tail, 

 possessing true limbs of indeed remarkable homological symmetry, 

 well developed lungs and voice, all the change in the circulation of 

 the blood implied by the presence of the lungs, and all the great 

 changes in the muscular and other systems of organs implied in the 

 use of well developed limbs and in making insects its only food, 

 while other Families of this same Class illustrate, in the mature 

 condition, almost every stage of the process by which so great a 

 change is accomplished. Nor can it be without a deep significance 

 that in all the higher Vertebrates — in Man himself, somewhat similar 

 metamorposes take place in intra-uterine life — the embryo having 

 gills (not fully developed) before it has lungs, although as the blood 

 is not aerated within the embryo they can have no direct use. 



All Vertebrates are Quadrupeds, and each limb, if complete, 

 has five digits, but while in the JJngulata many have but two well 

 developed digits to each limb, and in the Equine Family all but one 

 have become atrophied, in the Order Ophidia, the limbs are com- 

 pletely atrophied and functionless (with rare exceptions), and not 



* The tail is 11 inches long, and 3^ inches broad. It consists of 20 vertebraj, 

 and has a row of feathers along the sides. These few feathers are in pairs corres- 

 ponding with tlie number of the vertebrae, and diverge from the axis at an angle 

 of 'lo'" ; the last pair extends backwards nearly in a line with the last vertebrae, 

 and 3^ inches beyond it. The wing appears to have a two jointed finger. The 

 breadth of the wing was made by feathers as in birds, and not as in a Pterodactyl 

 by an expanded membrane. The feet are like those of Birds. 



