652 THE AMERICAN NATURALIST. [VoL XXXII. 
those long ages of preparation which ended in the crisis or 
cataclysm which closed the Paleozoic, the amphibian type was 
slowly being evolved in the swamps and bayous of the low- 
lands of the Devonian, whose vegetation so nearly anticipated 
that of the Carboniferous, from some Devonian! or late Silurian 
ganoids, from which diverged on the one hand Dipterus and 
the colossal lungfish (Dinichthys and Titanichthys) of the 
Devonian, and perhaps on the other the labyrinthodonts, which 
may have sprung’ from some crossopterygian fish like Polyp- 
terus, and whose pectoral and ventral fins became adapted for 
terrestrial locomotion. The type evidently was brought into 
being, provoked by, and at the same time favored by, the 
great extent of low coastal swampy land and bodies of fresh 
water which bordered the Atlantic seaboard from the Silurian 
time on. 
How the amphibian type arose from the ganoid stock is a 
matter of conjecture. It may, however, be surmised that 
certain of the lungfishes or forms like them, adapted for 
breathing the air direct when out of the water in the dry 
season, instead of remaining in their mud cells waiting for the 
rains to fill the lakes or swell the rivers, attempted, like the 
Anabas, or climbing fish, to migrate in schools overland; or, 
like that fish which is said to have become “so thoroughly a 
land animal that it is drowned if immersed in water,” ? it may 
have become confined to the land, and, losing its gills, used its 
lungs only. As the final result of its efforts to walk over the 
damp soil and mud of swampy regions, the uniaxial fins may 
have developed, through the strains and pressures of supporting 
the clumsy body, into props with several leverage systems ; the 
basalia instead of remaining in one place, as in a fish’s fin, 
spreading out and becoming digits to support the weight and 
steady the body while walking. This process was not confined 
to one or to a few individuals, but, as Lamarck insists in the 
cases he mentions, it affected all the individuals over a large 
area. Those individuals with incipient limbs became erased or 
1 Certain footprints recently discovered in the Upper Devonian show that the 
type had become established then, at least vertebrates with legs and toes. 
2 Parker and Haswell’s 7ext-Book of Zoology, vol. ii, p. 220. 
