AERIAL—EVOLUTION OF FAUNAS. 801 
We cannot believe in any abrupt transition from the shore to derra 
forma. It has been a slow ascent, slow as the origin of dry land 
itself. Thus mud-inhabiting worms, dwellers in damp humus, bank- 
frequenting animals, those which find a safe retreat in rottenness or 
inside bolder forms, dot the path from the shore inland. Many have 
lingered by the way, many have diverged into cul-de-sacs, many have 
been content to keep within hearing of the sea’s lullaby, which soothed 
them in their cradles. 
Simroth, in his work on the origin of land animals, seeks to show 
that hard skins, cross-striped. muscle, brains worthy of the name, red 
blood, and so on, were acquired as the transition to terrestrial life 
was effected. Let us take the last point by way of illustration. Iron 
in some form seems essential to the making of hemoglobin, but iron 
compounds are relatively scarce and not readily available in the sea ; 
they are more abundant in fresh water, and yet more so as the land is 
yeached. Therefore it is suggested that it was as littoral animals 
forsook the shore for the land, va fresh-water paths, that iron, in some 
form, entered into their composition, became part and parcel of them, 
helped to form heemoglobin or some analogous pigment, and thus opened 
the way to a higher and more vigorous life. 
Aerial,.—The last region to be conquered was the air. 
Insects were the first to possess it, but it was long before 
they were followed. The flying-fishes vibrated their fins 
above the foam as they leapt; the web-footed tree-frogs, 
Draco volans with its skin spread out on elongated ribs, and 
various lizards, began to swoop from branch to branch ; 
some of the ancient Saurians flopped their leathery skin- 
wings ; a few arboreal mammals essayed what the bats 
perfected ; and the feverish birds flew aloft gladly. 
Perhaps a keen struggle among insects, or such events as floods, 
storms, and lava-flows would prompt to flight; perhaps it was the 
eager males who led the way; perhaps the’ additional respiratory 
efficiency, produced by the outgrowth of wings, gave these a new use. 
Perhaps the high temperature of birds—an index to the intensity of 
their metabolism—may have had to do with the development of those 
most elaborate epidermic growths which we call feathers. But we must 
still be resigned to a more or less ingenious ‘‘ perhaps.” 
Evolution of faunas.—The problem of the evolution of 
faunas is still beyond solution, but various possibilities may 
be stated. 
(a) According to Moseley, ‘“‘the fauna of the coast has not only 
given origin to the terrestrial and fresh-water faunas, it has throughout 
all time, since life originated, given additions to the Pelagic fauna in 
return for having received from it its starting-point. It has also received 
some of these Pelagic forms back again to assume a fresh littoral 
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