r" 



6 AMPHIBIA. 



those points which may be illustrated by a reference to our own 

 native species. The most striking external character by 

 which the whole of these animals are distinguished is the 

 naked skin. Whilst all the true Reptilia are covered by 

 some hard and corneous or, at least, coriaceous modification 

 of the cuticle, which appears in the form of plates, as in the 

 Crocodiles and Tortoises, and in that of scales, as in the 

 Lizards and Serpents, the Amphibia have no vestige of 

 such a structure ; the skin being in all cases soft and smooth, 

 and in many instances always more or less moist. Some of 

 them, as the Salamanders and the Toads, have a number of 

 cutaneous glands which secrete a viscid fluid, which is said to 

 be more or less acrid and irritating. This is most conspi- 

 cuous in the common Salamander of Europe, which when 

 irritated will often throw out from these glands a quantity of 

 such wdiite and tenacious fluid. Now the acrid quality of 

 this secretion forms the sole ground for the reputed poison- 

 ous character of these animals ; for it is a well-ascertained 

 truth that not one of them possesses any organ by which 

 poison can possibly be communicated. The cuticle is fre- 

 quently shed, and in various modes, according to the habits of 

 these species. Thus the cuticle of the Frog and the Water 

 Newt comes off in shreds in the water ; whilst that of the 

 Toad is removed at once by the exertions of the animal, 

 comes away whole, and is swallowed at one gulp. Of this 

 very curious fact the details will be found in the description 

 of the common Toad. 



But the most interesting circumstance connected with the 

 functions of the integuments of these animals, or indeed with 

 any part of their economy, is their cutaneous respiration ; or, 

 in other words, the power which the surface of the skin pos- 

 sesses of effecting those changes in the blood which are 

 usually performed by the lungs or branchia?. It was ascer- 

 tained by Spallanzani, that the skin of the Frog gave out 



