AERIAL EVOLUTION OF FAUNAS. 801 



We cannot believe in any abrupt transition from the shore to terra 

 firma. 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 haemoglobin, 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 

 reached. Therefore it is suggested that it was as littoral animals 

 forsook the shore for the land, via fresh-water paths, that iron, in some 

 form, entered into their composition, became part and parcel of them, 

 helped to form haemoglobin 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 



