1880.] _ A Review of the Modern Doctrine of Evolution. 265 
derive any living type from the osseous fishes of the present or 
past ages (Hyopomata): to find the origin of Batrachia, we must 
pass below these to more generalized and older forms, the Dipnot, 
a class whose position in the system was for years a controverted 
point. We cannot obtain Mammalia from any of the existing 
types of reptiles, but we must go back to the Permian period, and 
trace their outlines in the Zheromorpha of that day. In spite of 
the prophetic resemblance of these remarkable animals, they are 
inferior to later Reptilia in the structure of their vertebral column, 
and display resemblance to some of their immature stages, as 
well as to those of the Mammalia. Among mammals we cannot 
derive monkeys from Carnivora or Ungulata, nor the latter from 
each other, but can only trace their close approximation in the 
Bunotherian types of the Lower Eocene. So with the great 
divisions of Ungulata; Preboscidians, Hyrax, and tHe even and 
odd-toed orders must all be traced to the unspecialized Amdlypoda, 
with small brains and five-toed plantigrade feet, as their ancestors.’ 
It is easy to perceive that the generalization and plasticity of all 
these forms has furnished the ground of their ancestral relation. 
Weare now in a position to comprehend more clearly the 
general nature of evolution. The doctrine of the unspecialized 
teaches that the perfection produced by each successive age has 
not been the source or parent of future perfection. The types 
which have displayed the most specialized mechanism have either 
passed away, or, undergoing no change, have witnessed the pro- 
gress and ultimate supremacy of those who were once their 
inferiors. This is largely true of animals which have attained great 
bulk. Like those with perfected weapons, they have ever been 
Superior to the attacks of other animals in their day, and doubt- 
less led, so long as food abounded, lives of luxurious indolence. 
With change or diminution of food, such huge beasts would be the 
first to succumb, and it is a fact that no type of land animals has- 
maintained great size through many geologic changes. It is true - 
that all of the lines of ancestry of the existing higher Mammalia, 
as the subdivisions of the Carnivora, Ungulata and Quadrumana, 
which we know in detail, commenced with types of small s size and 
correspondingly little muscular power. 
me important conclusions may be derived from pee ke 
"See the origin of types of Mammalia educabilia, a mar Philadelphia, 
1874. This view was subsequently expressed by Huxley. 
VOL, XIV.—No, IV, 18 
