556 AMPHIBIA. 



of that transition from aquatic to aerial respiration, which 

 must have marked one of" the most momentous epochs in 

 the evolution of Vertebrates. 



Classification of Amphibia. 

 Order Anura or Ecaudata (tailless as adults). 



Sub-order Phaneroglossa (tongue present). 



Series A. Arcifera (see p. 536), e.g. the toothless toads (Bu/o) ; 

 the tree-frogs (Hyla), with adhesive glandular discs 

 on the ends of the digits ; the obstetric frog [Alyles) ; 

 Bombinator, PelobcUes, and others. 

 Series B. Firmisternia (see p. 536), the frogs proper (Ranidae), 

 e.g. the grass-frog (R. temporarid), the edible frog 

 (R. esculenta), the N. American bull-frog (R. cates- 

 biana), sometimes 8 in. in length, and with a 

 sonorous croak. 



Sub-order Aglossa (tongueless). 



The Surinam toad (Pipa americana), in which 

 the eggs develop in pouches on the back of the 

 female ; and the allied Ethiopian genus Xenopus, 

 with a tentacle extending backwards on each side 

 of the head. 



Order Urodela or Caudata. 



The tail persists in adult life ; the body is elongated ; the limbs are 

 weak when compared with those of Anura. 



(a) Forms like Proteus : — Two extant genera, Proteus and Necturus, 



both with persistent gills. Several spieces of Proteus inhabit 

 the water in the caves of Carinthia and Dalmatia in Austria. 

 The gills persist ; there are two pairs of limbs. The eyes are 

 degenerate ; the colours are pale, as we should expect in cave- 

 animals. Two species of Necturus (or Menobranchus) occur 

 in N. America, in rivers and lakes. 



(b) Forms like Siren : — Two extant genera, Siren and Pseudo- 



branchus, both N. American, both with persistent gills, with 

 only the anterior limbs, 

 (r) Forms like the newts and salamanders : — The N. American 

 Amphiuma, with two pairs of rudimentary legs, with a slit 

 persisting in adult life as a remnant of the gilled state ; Megalo- 

 batrachus or Cryptobranchus maximus, the largest living 

 Amphibian, found in Japan and Thibet, attains a length of 

 3 ft. ; Amblystoma and its gilled form the Axolotl ; Desmo- 

 gnathus fusca, the common water salamander of the United 

 States, lays its eggs in a wreath which one of the sexes twines 

 round its body ; Salamandra maculosa and S. atra, both 

 European, both viviparous ; the newts — Triton or Molge — of 

 which Triton alpestris becomes sexually mature while still 

 larval. 



