164 NATURAL SELECTION vn 



mediate between them both. The illustration of the duck 

 and the gull is therefore misleading ; one of these birds has 

 not been derived from the other, but both from a common 

 ancestor. This is not a mere supposition invented to support 

 the theory of natural selection, but is founded on a variety of 

 indisputable facts. As we go back into past time, and meet 

 with the fossil remains of more and more ancient races of 

 extinct animals, we find that many of them actually are 

 intermediate between distinct groups of existing animals. 

 Professor Owen continually dwells on this fact : he says in 

 his Palceontology, p. 284 : "A more generalised vertebrate 

 structure is illustrated, in the extinct reptiles, by the affinities 

 to ganoid fishes, shown by Ganocephala, Labyrinthodontia, and 

 Ichthyopterygia ; by the affinities of the Pterosauria to birds, 

 and by the approximation of the Dinosauria to mammals. 

 (These have been recently shown by Professor Huxley to 

 have more affinity to birds.) It is manifested by the combina- 

 tion of modern crocodilian, chelonian, and lacertian characters 

 in the Cryptodontia and the Dicynodontia, and by the com- 

 bined lacertian and crocodilian characters in the Thecodontia 

 and Sauropterygia." In the same work he tells us that " the 

 Anoplotherium, in several important characters, resembled 

 the embryo Ruminant, but retained throughout life those 

 marks of adhesion to a generalised mammalian type ; " and 

 assures us that he has " never omitted a proper opportunity 

 for impressing the results of observations showing the more 

 generalised structures of extinct as compared with the more 

 specialised forms of recent animals." Modern palaeontologists 

 have discovered hundreds of examples of these more generalised 

 or ancestral types. In the time of Cuvier, the Kuminants 

 and the Pachyderms were looked upon as two of the most 

 distinct orders of animals ; but it is now demonstrated that 

 there once existed a variety of genera and species, connecting 

 by almost imperceptible grades such widely different animals 

 as the pig and the camel. Among living quadrupeds we can 

 scarcely find a more isolated group than the genus Equus, 

 comprising the horses, asses, and zebras ; but through many 

 species of Paloplotherium, Hippotherium, and Hipparion, and 

 numbers of extinct forms of Equus found in Europe, India, 

 and America, an almost complete transition is established with 



