CLASSIFICATION OF AMPHIBIA 677 



111 the reduction of the tail the epidermis thickens and is partly cast, 

 partly dissolved ; the muscles break up, and their substance undergoes 

 intracellular digestion or is dissolved in the body juices ; the notochord 

 is repeatedly bent on itself and is also disrupted ; the same is true of 

 nervous system and blood vessels. It is a pathological process which 

 has become normal. Some credit the phagocytes with playing a very 

 important part in the reduction of the tail ; but others restrict theur 

 function to engulfing solid particles, such as pigment granules, and say 

 that most of the material degenerates until it becomes almost hquid, 

 when it passes directly into the vascular fluid. 



In many respects the development of the tadpole is very 

 interesting, especially because it is a modified recapitulation 

 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 



The adults have no tail or external gills or open gill-clefts. There 

 are always four limbs. There are few (5-9) vertebrae, and no ribs 

 except in Discoglossidoe. 



Sub -order Phaneroglossa.— Tongue present ; the Eustachian tubes 

 open separately into the pharynx. 

 Series A. Arcifera, e.g. the toothless toads (Bufo) ;. the tree-frogs 

 {Hyla), with adhesive glandular discs on the ends 

 of the digits ; the obstetric frog {Alytes) ; Bombinator, 

 Pelobates, and others. 

 Series B. Firmisternia, the frogs proper (Ranidae), e.g. the grass- 

 frog {R. temporaria), the edible frog {R. esculenta), 

 the N. American bull-frog (R. catesbiana). 

 Sub-order Aglossa.— Tongueless ; the Eustachian tubes have a 

 common median aperture into the pharynx. The Surinam 

 toad {Pipa americana), and the allied African genus 

 Xenopus. 



Order Urodela or Caudata 



The tail persists in adult Hfe ; the larval gills and gill-sHts may also 

 persist ; the limbs are weak when compared with those of Anura, and 

 the hind pair may be absent. There are numerous (37-98) vertebra, 

 amphicoelous or opisthocoelous. 



Family i. Amphiumidae. — The N. American Amphiuma, with two 

 pairs of rudimentary legs, with a slit persisting in adult life 

 as a remnant of the gilled state ; Cryptobranchus maximus, 

 the largest living Amphibian, found in Japan and Thibet, 

 attains a length of over 3 ft. 



