22 



don from the American Cretaceous, the teeth are entirely absent, 

 and the tail is a mere rudiment. In the gradual loss of the 

 teeth and tail, these reptiles followed the same path as Birds, and 

 might thus seem to approach them, as many have supposed. 

 This resemblance, however, is only a superficial one, as a study 

 of the more important characters of the Pterodactyls shows 

 that they are an aberrant type of Reptiles, totally oft' the line 

 through which the Birds were developed. The announcement 

 made not long since in Europe, and accepted by some American 

 authors, that the Plerosauria, in consequence of certain points 

 in their structure, were essentially Birds, is directly disproved 

 by American specimens, far more perfect than those on which 

 the conclusion was based. 



It is now generally admitted by biologists who have made 

 a study of the vertebrates, that Birds have come down to us 

 through the Dinosaurs, and the close affinity of the latter 

 with recent Struthious Birds will hardly be questioned. The 

 case amounts almost to a demonstration, if we compare, with 

 Dinosaurs, their contemporaries, the Mesozoic Birds. The 

 classes of Birds and Reptiles, as now living, are separated by a 

 gulf so profound that a few years since it was cited by the 

 opponents of evolution as the most important break in the 

 animal series, and one which that doctrine could not bridge 

 over. Since then, as Huxley has clearly shown, this gap 

 has been virtually filled by the discovery of bird-like Reptiles 

 and reptilian Birds. Compsognathus and Archceopteryx of the 

 Old World, and Ichihyornis and Hesperornis of the New, are 

 the stepping stones by which the evolutionist of to-day leads 

 the doubting brother across the shallow remnant of the gulf, 

 once thought impassable. 



It remains now to consider the highest group of the Animal 

 Kingdom, the class Mammalia, which includes Man. Of the 

 existence of this class before the Trias we have no evidence, 

 either in this country or in the Old World, and it is a significant 

 fact that at essentially the same horizon in each hemisphere, sim- 



