COMMON FROG. 85 



If in the natural system of animals we must look for the 

 typical representative of any group in that form in which the 

 distinctive characters of the whole group are most obviously 

 and unequivocally developed, — a test insisted upon, I be- 

 lieve, by all who have even professed to believe in the ex- 

 istence of sucli types of form, — it is in the family Ranidts 

 that we may expect to find the typical character of the pre- 

 sent class of animals ; and the truth of this test is not in- 

 validated by the absurd and even ludicrous instances of its 

 breach, of which some of the most strenuous asserters of the 

 principle have been guilty. To apply to this test only one 

 or two of the structural or physiological peculiarities of the 

 class. The most remarkable and important of all is the 

 change, which has already been mentioned, from the con- 

 dition of a fish to that of a reptile ; and in this respect, whilst 

 we must consider the permanent pisciform condition of the 

 Proteus, the Siren, and others, which retain their branchial 

 respiration throughout life, as an abnormal form leading to- 

 wards the fishes, and the Cacilia, on the other hand, as probably 

 approximating the Ophidian Reptilia ; the caducibranchiate 

 groups — and especially the present family — exhibit the phe- 

 nomena of this metamorphosis to the greatest extent, the 

 change which they undergo being certainly more complete 

 than that of any of the other forms. The cutaneous respi- 

 ration is another peculiar characteristic of the class ; and 

 there is no doubt that this function also is enjoyed by the 

 Frogs in the highest degree. 



The innocent and very useful species about to be de- 

 scribed, is one of the most common of our vertebrated ani- 

 mals. It is found in almost all parts of this island, wher- 

 ever there is a river or a pool, or even sufficient shade to 

 maintain the degree of moisture necessary to preserve the 

 respirable condition of the skin ; for the presence of a con- 

 siderable quantity of water, although requisite for the deve- 



