576 PALEONTOLOGY 



same method of reasoning, a method which was first clearly outlined 

 by Huxley, namely, by the more or less ideal reconstruction of the 

 primitive central form from which radiation has occurred. This is a 

 very difficult matter where the primitive central form is not preserved 

 either living or as a fossil. In such instances we may by analysis of 

 all the existing forms prophesy the structure of the primitive central 

 form, as Huxley, 1 Kowalevsky, 2 and Cope 3 did in the case of the 

 hoofed animals, a prophecy which was nearly fulfilled by the discovery 

 in northern Wyoming of Phenacodus. In other more fortunate cases 

 the primitive central form survives both living and fossil, as in the re- 

 markable instance of Paleohatteria of the Permian and the tuatera 

 lizard (Hatteria) of New Zealand, which gave rise to the grand 

 adaptive radiation of the lizards, mosasaurs, dinosaurs, crocodiles, 

 phytosaurs, and probably of the ichthyosaurs. 



In the reconstruction of these primitive central forms, we must 

 naturally discriminate between analogy and homogeny, and paleon- 

 tologists are not agreed in all cases on such discrimination. On the 

 border region, in fact, where the primitive central forms are still un- 

 known, where analogy has reached its most perfect climaxes and imi- 

 tations, are found the great paleontological controversies of to-day. 

 For example, among the paleozoic fishes, the armored ostracoderms 

 (Pteraspis, Cephalaspis, Pterichthys) and the arthognaths (Coccos- 

 teus, Dinichthys) by some authors (Hay, 4 Regan, 5 Jaekel 6 ) are placed 

 in the single group of placoderms, while by other authors (Smith 

 Woodward 7 and Dean 8 ) they are regarded as entirely independent and 

 superficially analogous groups. The dipnoi, or lung fishes (Ceratodus, 

 Protopterus) , present so many analogies with the amphibians (sala- 

 manders and frogs) that they were long regarded as ancestors of the 

 latter; but more searching anatomical and paleontological analyses 

 and recent embryological discoveries have proved that the dipnoi and 

 amphibia are parallel analogous groups descended alike from the 



1 T. H. Huxley, The Anniversary Address of the President, Quarterly Journal 

 of the Geological Society, London, vol. xxvi, 1870. 



2 Kowalevsky, Osteology of the Hyopotamidae, Philosophic Transactions, 1873, 

 p. 69; Versuch einer natiirlichen Classification der fossilen Hufthiere (Monographic 

 der Gattung Anthracotherium Cuv.) Paleontographica, N. F., n, 3 (xxn), 1873. 



s E. D. Cope, On the Homologies and Origin of the molar teeth of the Mammalia 

 Educabilia, Journal of the Academy of Natural Sciences, Philadelphia, March, 

 1874, pp. 20, 21. 



4 O. P. Hay, Bibliography and Catalogue of the Fossil Vertebrata of North America, 

 Bulletin of U. S. Geological Survey, no. 179, 1902, p. 253. [N. B. Dr. Hay includes 

 with the Arthrodira the Antiarcha alone of the Ostracoderms.] 



* C. Tate Regan, The Phylogeny of the Teleostomi, Ann. and Mag. Natural 

 History, ser. 7, vol. xin, May, 1904, pp. 340-346. 



* O. Jaekel, Ueber Coccosteus und die Beurtheilung der Placodermen, Sitzungs Ber. 

 d. Ges. Naturforchender Freunde, Berlin, Jahrg. 1902, no. 5. 



7 A. Smith Woodward, Outlines of Vertebrate Paleontology, Cambridge, 1898, 

 p. 64, 3. 



8 Bashford Dean, The Devonian Lamprey Paleospondylus, with Notes on the 

 Systematic Arrangement of the Fish-like Vertebrates. Memoirs, New York Academy 

 of Sciences, vol. n, pt. i, 1900, p. 22 et seq. 



