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 



