CHARACTERS AND POSITION 5 



Numbere 1 (6), 1 (c), 2, 3, 4 and 12 separate the Amphibia from the Fishes. 



Numbers ], 6 (b), 7, 8, 9, II, 13, 15 sepaiate them from the Reptiles, 

 Birds, and >[amma]s. 



Number 2 separates them ft-om the Fishes, Reptiles, and Birds. 



Number 5 separates them from the Mammals. 



Number 6 (a.) separates them from the Fishes (excl. Dipnoi), Birds and 

 Mammals. 



We can, therefore, very easily define all the Amphibia, both 

 recent and extinct, by a combination of the characters enumerated 

 above. For instance, by the combination of numbers 2, 3 or 4 

 with either 7, 8, 9, 11, 13 or 15. 



Amplhicondylous Aimmnia would be an absolutely correct and 

 all-sufficient diagnosis, but it would be of little use in the deter- 

 mination of adult specimens ; and the tetrapodous character is of 

 no avail for Apoda. Ampliicondylous animals ivithout an infra- 

 cranial hypoglossal nerve is a more practical diagnosis. 



In the case of living Urodela and Anura the absence of any 

 scales in the skin affords a more popular character ; it is unfor- 

 tunately not applicable to the Apoda, many of which possess 

 dermal scales, although these are hidden in the imbricating 

 transverse rings of the epidermis ; and the frequent occurrence of 

 typical scales of both ecto- and meso-dermal composition in many 

 of the Stegocephali forces us to discard the scales, or rather their 

 absence, as a diagnostic character of the class Amphibia. The 

 same applies to the mostly soft, moist, or clammy, and very glan- 

 dular nature of the skin. 



The position of the class Amphibia in the Phylum Verte- 

 brata. — There is no doubt that the Amphibia have sprung froTu 

 fish-like ancestors, and that they in turn have given rise to the 

 Keptilia. The Amphibia consequently hold a very important 

 intermediate position. It was perhaps not a fortunate innova- 

 tion when Huxley brigaded them with the Fishes as Ichthyopsida, 

 thereby separating them more from the b'auropsida ( = Eeptilia 

 and Aves), than is justifiable, — perhaps more than he himself 

 intended. The connecting-link, in any case, is formed by the 

 Stegocephali ; all the recent Orders, the Apoda, Urodela, and 

 Anura, are far too specialised to have any claims to the direct 

 ancestral connections. The line leading from Stegocephali to 

 fossil Eeptiles, notably to such Proreptilia as Eryops and 

 Cricotus, and even to the Lepospondylous Prosauria, is extremely 

 gradual, and the steps are almost imperceptible. Naturally, 



