6io THE SCIENTIFIC MONTHLY
ihrougb and form the current. The strength of the current varies from four volU in Mormyrua up to as much as 250 or more in Qym- notus, the electric eel, and consists of a series of shocks discharged 3/1000 of a second apart.
ZrOLUTIOK OF THE AMPHIBIA
A single impression of a three-toed footprint {Thinopua antiquus) in the Upper Devonian shales of Pennsylvania constitutes at present the sole palcontologic proof of the period of transition from the fish
��Fic.
��FOOTPBINt
��THE Rari.iest Knohth Liubbd AMUAt^, an AmphLblnn from tbt Vpp^r npionlan of Petrn- ■jlvanlB, Type In th« Pe«- botly Muspum of Yale llnlrer- Blty. Pbotograpb of caat pre- Rpnt^ to the AmfrkaD Mu- apum by tb» Peabody Muaeum.
�� ��I pKiHinvK
FEB Devon II If TtHB (Pentadacliitoldea, Tftrapoda}. wltb 1arg«. BO] Idly rooted ■kull. tour limba. and Btb flngen on enrh of the fore and bind fwt. After FrllBch.
��tj'pe to the amphibian type. This took place in Lower Devonian if not in Upper Silurian time. The adaptive radiation of these primordial Amphibia probably began in Middle Devonian time and extended through the great swamp, coal-forming period of the Carboniferous, which afforded over vast areas of the earth's surface ideal conditions for amphibian evolution, the stages of which are best preserved in the Coal Measures of Scotland, Saxony, Bohemia, Ohio and Pennsylvania, and have been revealed through the studies of von Meyer, Owen, Pritsch, Cope, Credner and Moodie. The earliest of these terrestrio-aquatic
�� �
