THE EVIDENCE OF THE CENTRAL NERVOUS SYSTEM 23 
reptiles arose from the race which was then predominant on the earth 
—the Amphibia. 
Again, another point of great interest is seen here, and that is 
that these Labyrinthodonts, as Huxley has pointed out, possess 
characters which bring them more closely than the amphibians of 
the present day into connection with the fishes; and further, the 
fish-like characters they possessed are those of the Ganoids, the 
Marsipobranchs, the Dipnoans, and the Elasmobranchs, rather than 
of the Teleosteans. 
Now, it is a striking fact that the ancient fishes at the time when 
the amphibians appeared had not reached the teleostean stage. The 
ganoids and elasmobranchs swarmed in the waters of the Devonian 
and Carboniferous times. Dipnoans and marsipobranchs were there, 
too, in all probability, but teleosteans do not appear until the 
Mesozoic period. The very kinds of fish, then, which swarmed in 
the seas at that time, and were the predominant race before the 
Carboniferous epoch, are those to which the amphibians at their first 
appearance show the closest affinity. Here, again, the same law 
appears ; from the predominant race at the time, the next higher 
race arose, and arose by a most striking modification, which was the 
consequence of altering the medium in which it lived. By coming 
out of the water and living on the land, or, rather, being able to live 
partly on land and partly in the water, by the acquisition of air- 
breathing respiratory organs or lungs in addition to, and instead of, 
water-breathing organs or gills, the amphibian not only arose from 
the fish, but made an entirely new departure in the sequence of 
progressive forms, 
This was a most momentous step in the history of evolution — 
one fraught with mighty consequences and full of most important 
suggestions, 
From this time onwards the struggle for existence by which 
upward progress ensued took place on the land, not in the sea, and, 
as has been pointed out, led to the evolution of reptiles from am- 
phibians, birds and quadrupedal mammals from reptiles, and man 
from quadrupeds. In the sea the fishes were left to multiply and 
struggle among themselves, their only opponents being the giant 
cephalopods, which themselves had been evolved from a continual 
succession of the Mollusca. For this reason the struggle for existence 
between the fishes and the higher race evolved from them did not 
