Page:The Scientific Monthly vol. 3.djvu/617

 ORIGIN AND EVOLUTION OF LIFE 6ii

types have not only a dual breathing system of gilU and longs but s dual motor equipment of limbs and a propelling median fin in the tail region.

So far as known primordial Amphibia in body form were chiefly of the small-headed, long-bodied, Bmall-limbed, tail-propelled type of the modern salamander and newt. The large-headed, short-bodied types {Amphibamus, Pterophlax) were primitive. In Upper Carboniferous and early Permian time the terrestrial forms began to be favored by the land elevation and recessioD of the eea which distinguished the close of the Carboniferous and early Permian time. Under these varied zonal

���Fig. 21. Descbnt or the Aufiiibia in which tub Fin is TiUNSrOBUBD into a liiUD (TMnopua), from an Hncestral Qanold flsb atock of Sllurlsn agt tbrougb the frlage-Bnned Ganoids. Prom thla group diverse the anceBton o( the Beptlllft and the ■alamHtider-llke AmphlblaaH which give rUe to the vsrlom salainaiider trpea. also to brauchea oC Umblesa and Boake-IIke forms (AUtopoda, modern Ccedlluie). Tbe otber great branch of the Bolld-Bknlled Amphibia, the Btegocephala. was widespread all over the northern cootlnenta la Permian and Trlaaalc time (Crtcottu, Eryopi), and (rom this stock descended the modern frogi and toads ^Al^ura). Prepared for the aathor bj Wm. K. Gregory,

��conditions, aquatic, palustral, terrestrio-aquatic, fossorial and terres- trial, the Amphibia radiated into several habitat zones and adaptive phases, thus recapitulating all the chief types of body form which had previously evolved among the fishes and anticipating many of the types of body form which were to evolve among the Reptilia. One ancestral feature is a layer of superficial body scales derived from those of their

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