204 The American Geologist. October, 1905. 
the definite or determinate "origin 1 and development of cer- 
tain at least of the new adaptive structures, apparently, but 
not certainly according to the principle to which Waagen 
applied the term mutation". The mutation of the palaeon- 
tologist, however, is quite distinct from the phenomena of 
minute saltations to which de Yries has applied Waagen's 
term in his valuable experiments 1 . 
Potential of similar evolution — In connection with ana- 
logous, but especially with partially determinate evolution, 
we not only have the similarly moulding influences of simi- 
lar habits, and the action of the various factors of evolution" 
which we cannot stop to discuss, but clear evidence of the 
existence of a potential of similar evolution, a kind of latent 
homology which determines that when certain structures 
are to appear among animals independently derived from a 
common stock, they will appear at certain definite points 
and not at random. For example, the genesis of the rudi- 
ment of the horn in three independent phyla of Eocene titan- 
otheres is at exactly the same point, namely, at the point of 
junction of the frontals with the nasals at the side of the 
face just above the eye. 
The polyphyletic law. — Partly as an outgrowth of the 
synthesis of the above principles and partly as the result of 
new discoveries and the closer study of types already known 
is the full recognition of the polyphyletic law. 3 If we ex- 
amine the phylogenies of Huxley and Cope, and even those 
of more recent writers (Scott, Osborn, Wortman) of a 
decade ago, we find that the attempt is made for example, 
to trace the pedigrees of the horses and rhinoceroses in a 
monophyletic manner. The first known instance of this kind 
was Huxley's pedigree of Eqmis through Hipparion, Avchi- 
therium and Palaeotherium, all of which are now known, to 
belong to entirely distinct phyla. Another instance was 
1 Osborn, H. F. The Palaeoniological Evidence for the Transmission 
of Accquired Characters. Amer. Naturalist, vol. xxiii, 18S9. p. 562. 
2 Scott, W. B. On Variations and Mutations. Amer. Jour. Sci. vol. 
xlviii. Nov. 1894, pp. 355-374. 
1 Elsewhere this profound difference between palaeontological muta- 
tions and the mutations of de Vries is carefully pointed out. See '-Osborn 
Present Problems of Palaeontology", address before St. Louis Congress 
of Science and Art, September, 1904, first printed in Popular Science 
Monthly, December, 1904. 
2 Osborn, H. F. St. Louis Address. Loc . cit. supra. 
3 Osborn, H. F. The Perissodactyls typically polyphyletic. Science, 
N. S., vol. xvi, 1902, p. 715. 
