DARWINISM AND EVOLUTION. 1 9 



We learn from oolitic strata that before the advent of birds 

 there existed saurians that sometimes walked on their hind limbs, 

 and others that hopped on the ground after the manner of a 

 sparrow. There were flying lizards with short tail, keeled 

 breast-bone, and a pneumatic skeleton (its cavities filled with air) 

 like a bird; while the feathered Archseopteryx, with its 20 caudal 

 segments or tail-bones and its sternum without a keel, in these 

 points resembled a reptile. 



With respect to saurians themselves, we may contrast the 

 huge head of Magalosaurus (fig. G. See next page) with the small 

 skull of Pterodactyles, one of whom (P. Crassirostris, fig. If.) had 

 jaws armed with socketed teeth, while another (P. Pteranodon) had 

 toothless jaws encased in a bird-like beak ; and as regards birds 

 alone, the jaws of the Ichthyornis dispar, with recurved teeth 

 sunk in distinct sockets, and those of Hesperornis regalis, with a 

 terminal horny envelope, but also furnished with numerous conical 

 teeth sunk in a continuous groove, may be compared with the 

 strongly denticulate jaws of Odontopteryx toliapicus, (fig. I.) and 

 these, in turn, with the roughened mandibles of the existing 

 Spur-winged Goose (fig. J.) 



3. Homology deals with organs that are structurally alike, but 

 which discharge different functions. The fin of a seal, the wing 

 of a bird, the foreleg of a dog, and the arm of a man, though each 

 performs a different office, are all built up of similar bony elements, 

 which bear a striking and sometimes a close resemblance to each 

 other. Some years ago, a bone which was found in the Victoria 

 cave in Yorkshire, was declared by Professor Busk to be a human 

 fibula ; but after a while he saw reason for thinking that it was the 

 fibula of a cave bear. The present writer has seen this fibula, and 

 by the side of it the fibula of a man, and, though familiar with 

 human anatomy, he feels sure that he could not have told 

 one from the other. Why should there be such a close similarity 

 between the corresponding bones of animals of the same class 

 unless such animals are related by community of descent ? Why 

 should the possession of seven cervical vertebrae, or neck bones, 

 be a general characteristic of mammals, whether the neck be 

 immensely long as in the giraffe, or quite rudimentary as in the 

 whale. "If it be urged," says Mr. Spencer, "that though for 

 "the whale's neck one vertebra would have been equally good, 

 " and though for the giraffe's neck a dozen would probably have 

 " been better than seven, yet that seven was the number required 

 " to make mammals correspond to an arbitrary type, such a view 

 "is abruptly dissolved by the fact that this possession of seven 

 " cervical vertebrae is not an absolutely universal characteristic of 

 "the mammalian class." Such correspondences at once become 

 intelligible when they are regarded as due to community of descent, 

 or as instances of a wide reaching family likeness. 



