296 PHILOSOPHY OF ZOOLOGY. 



Heart with one auricle. 



BATRACHIA. 



The skin is naked, and usually lubricated by a mucous 

 secretion. The vertebra?, in some genera, are hollowed into 

 cups on each end like those of fishes. The ventricle is des- 

 titute of fleshy columns, and sends out the blood by one 

 opening. There is no external organ of generation in the 

 male. Fecundation is generally external, and the eggs are 

 deposited in the water. The young are hatched in that 

 element, and, at the first, possess external branchiae, which, 

 in one genus, are persistent, and continue to supply the 

 place of aerating organs, Avhile in the other genera, they 

 are absorbed when the lungs have acquired their proper 

 degree of development. 



A. Furnished with feet. 



a. Furnished with a tail. 



(1.) In the adult state, furnished with lungs. 



The lungs are in the form of two bags, with the walls im- 

 perfectly cellular or honeycombed. Free air is respired in 

 the immature state, when recently excluded from the egg, 

 the young are furnished with fimbriated processes on each 

 side of the neck, with apertures at the base, which serve as 

 gills. These are supported by cartilaginous arches. At 

 this period, the nose, which, in the adult, is the aperture 

 through which the animal breathes, is unconnected with the 

 mouth. As the animal reaches maturity, the connection 

 between the nose and throat is established ; the lungs be- 

 come developed, while the branchial cartilages coalesce, and 

 the gills are absorbed. The animal, if it resides in the wa- 

 ter, is obliged, at intei'vals, to come to the surface to re- 

 spire. 



Furnished with four feet. Toes destitute of claws. 



%^. SiVLAMAis'DKA. Salamander. The tail round, in the 



