AMPHIBIA. 2S5 



similar apparatus ; it is in general moist or 

 clammy, and in many cases is provided with 

 numerous glands which pour out a viscid secre- 

 tion. The outer skin, or epidermis, is sloughed 

 at irregular intervals like that of the Lizards and 

 Serpents. The form is generally more or less 

 lizard-like, but in one Order, that of the Frogs, 

 this form is lost at an early period of life. They 

 possess, in general, four limbs ; but, like the 

 Lizards, they shew a tendency to merge into a 

 serpentiform condition, by the lengthening of the 

 body, and loss of the hinder extremities in the 

 Sirens, and by the total absence of feet, and 

 snake-like contour of the CcscilicB. 



Most of the Amphibia undergo a metamor- 

 phosis, or change of form, which is connected 

 with a change in the character of their respiration 

 and in the medium in which they live. Thus the 

 Frog is, in its first stage of active existence, a 

 fish-like Tadpole, breathing the water by means 

 of gills, but afterwards undergoes a great change 

 of form, gradually acquires four well-developed 

 limbs, throws off* its tail, and at the same time 

 loses its external gills, and becomes an air-breath- 

 ing animal, possessed of internal lungs, and 

 capable of crawling on the land as well as swim- 

 ming in water. Some of the genera, indeed, 

 possess both series of respiratory organs during 

 their whole life, and are consequently Amphihia 

 in a more strict and literal sense, possessing a 

 capacity of living and breathing in two ele- 

 ments. 



The reproduction is effected by means of eggs, 

 which are numerous, more or less globular in 

 figure, pellucid, and destitute of a calcareous 



