RiAar’ EE T, 
AMPHIBIA, OR BATRACHIANS. 
‘(HOSE geographers who divide the world into land and sea over- 
look in their nomenclature the extensive geographical areas 
which belong permanently to neither section—namely, the vast 
marshy regions on the margins of lakes, rivers, and ponds, which 
are alternately deluged with the overflow of the adjacent waters, 
or are parched from the exhalations produced by summer heat ; 
regions which could only be inhabited by beings capable of living on 
land or in water—beings having both gills (through which they may 
breathe in water) and lungs (through which they may breathe on 
land.) The first order of Reptiles possesses this character, and hence 
its name of Amphibia, from éu¢!-fios, having a double life. 
The transition from Fishes to Reptiles is described by Professor 
Owen, with that wonderful power of condensation which he possesses, 
in the following terms :—“ All vertebrates, during more or less of 
their developmental life-period, float in a liquid of similar specific 
gravity to themselves. A large proportion, constituting the lowest 
organised and first developed forms of this province, exist and 
breathe in water, and are called fishes. Of these a few retain the 
primitive vermiform condition, and develop no limbs; in the rest 
they are ‘fins’ of simple form, moving by one joint upon the 
body, rarely adapted for any other function than the impulse 
or guidance of the body through the water. The shape of the 
body is usually adapted for moving with least resistance through 
the liquid medium. The surface of the body is either smooth and 
lubricous or it is covered with overlapping scales ; it is rarely de- 
fended by bony plates or roughened by tubercles. . Still more- 
rarely is it armed with spines.” Passing over the general economy 
of Fishes we come to the heart. ‘The heart,” he tells us, “ consists 
of one auricle receiving the venous blood, and one ventricle pro- 
pelling it to the gills or organs submitting that blood in a state of 
minute subdivisions to the action of aérated water. From the 
gills the aérated blood is carried over the entire body by vessels, 
