H. F. OSBORN — MAMMALIAN PALÆONTOLOGY 91 
however, is quite distinct from the phenomena of minute saltations to 
which de VRies has applied Waagex’s term in his valuable experiments". 
Potential of similar evolution. — In connection with analogous, but 
especially with partially determinate evolution, we not only have the si- 
milarly moulding influences of similar habits, and the action of the va- 
rious 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 determinesthat when certain structures 
are to appear among animals independently derived from a 
common stock, they willappear at certain definite points and 
not at random. For example, the genesis of the rudiment of the horn 
in three independent phyla of Eocene titanotheres 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 poly- 
phyletic law *. If we examine the phylogenies of Huxzey and Core, and 
even those of more recent writers (Scorr, OsBorx, Worruax) 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 Huxzey’'s pedigree of Æquus through 
Hipparion, Anchitherium and Palæotherium, all of which are now known 
to belong to entirely distinct phyla. Another instance was the compara- 
tively recent effort to trace all rhinoceroses through the Oligocene Acera- 
therium occidentale Leidy as the stem form. 
The polyphyletic law is an outgrowth of four different Kkinds of evi- 
dence. First, that the stem forms are very much older than we supposed 
them to be; we placed them in the Pliocene and Miocene, they have now 
been traced to the Oligocene and Eocene. Second, as a consequence 0} 
this, certain modern genera of mammals have their own ancestry, apart 
from that of closely related genera, as far back as the Oligocene and 
perhaps Eocene. The most conspicuous example of this is the tracing 
back of the Dholes (genus Cyon) among the Canidæ, to an Oligocene 
form, showing that Cyon separated from Canis in the Eocene (WorTMAN 
1 Elsewhere this profound difference between” palæontological mutations and the 
mutations of de Verres is carefully pointed out. See « OsorN Present Problems of 
Palæontology », address before St. Louis Congress of Science and Art, September, 
1904, first printed in Popular Science Monthly, December, 1904. 
? Os2orN, H. F. St. Louis Address. Loc. cit. supra. 
# OsBorx, H. F. The Perissodactyls typically polyphyletic. Science, N.S$., Vol. xvi, 
1902, p. 715. 
