Page:The Scientific Monthly vol. 3.djvu/620

 6i4 THE SCIENTIFIC MONTHLY

An opposite extreme of slender body structure is found in the active predaceous types of water-loving amphibianB such as Cricotus, of rapid tnovements, propelled by a long tail fin and with sharp teeth adapted to seizing an actively moving prey. This t}-pe retrogresses into the eel-like, bottom-loving Lysorophus with its slender skull, elongate body propelled by lateral swimming undulations, the limbs relatively useless. Corresponding to the bottom-living fishes are the large, sluggish, broad- faeaded, bottom-living amphibians, euch as Diplocaulus, with heads heavily armored, limbs small and weak, the l»dy propelled by lateral

��Pia, 25. Sklu.. xhd Vebtebsu. Column or DiplocaulM, a typlcsl lolld-, broad- headed AmpblblsD tram the Permlaa ol Dortbem Tciaa. Sp«clmm Id the Ametlcaa Maseuin of Natural HlEtory.

motions of the tail. There were also more powerful, slow-moving, long- headed, alligator-like, terrestrio-aquatic forms, such as the Archegc- saurus of Europe and the fully aquatic Trimerorackis of America. An extreme stage of terrestrial, ground-living evolution with marked reduc- tion of the use of the tail for propulsion is the large-headed Caccops, short-bodied, with limbs of medium size, but with feeble powers of pre- hension in the feet. Radiating around these animals were a number of terrestrial types exhibiting the evolution of dorsal protective armature and spines (Aspidosaurns) ; other types leaJ into the pointed-headed structure and pointed teeth of Tremaiopx.

��Editorial Note : The remaining parts of this Lecture will appear in December or January in book form under the title " Origin and Evolu- tion of Life," from the press of Charles Scribner's Sons.

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