144 Wisconsin Academy of Sciences, Arts^ and Letters. 



I 



vided with teeth set in grooves ; the wings were rudimentary and 

 useless, while the legs were very similar to those of modern div- 

 ing birds. Ichthjornis, a small flying bird, was stranger still, as 

 the teeth were in sockets, and the vertebrae biconcave, as in fishes 

 and a few reptiles." 



"It is obvious," says Huxley, "that the contrast between the 

 crocodile's leg on the one hand, and the bird's leg on the other, 

 is very striking. But this interval is completely filled up when 

 you study the character of the hinder extremities of those ancient 

 reptiles which are called the Dinosauria. In some of these, the 

 bones of the pelvis, and those of the hind limb, became extraordi- 

 narily similar to birds, especially to those of young or foetal birds. 

 Furthermore, in some of these reptiles, the fore-limbs become 

 smaller and smaller, and thus the suspicion naturally arises, that 

 they may have assumed the erect position. That view was en- 

 tertained by Mantel, and was also demonstrated to be probable 

 by your own distinguished anatomist, Leidy, but the discoveries of 

 late years show that in some of these forms the fact was actually 

 so ; that reptiles once existed which walked upon their hind-legs as 

 birds now do. The Compsognathus longipes (Wagner) must as- 

 suredly have walked about upon its hind-legs, bird' fashion. Add 

 to this feathers, and the transition would be complete." 



It is now generally admitted by biologists " who have made a 

 study of the vertebrates," continues Marsh, " 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 Di- 

 nosaurs, their contemporaries, the Mezozoic birds. Compsognathus 

 and Archaeopteryx of the old world, and Ichthyornis and Hes- 

 perornis of the new, are the stepping-stones by which the evolu- 

 tionist of to-day leads the doubting brother across the shallow 

 remnant of the gulf, once thought impossible." 



Although this kind of evidence is far weightier than that upon 

 which men generally base their conclusions regarding important 

 propositions, it is not that kind of evidence which might be called 

 demonstrative. That is to say, it might be demanded " that we 

 should find the series of gradations between one group^of animals 



