CLASSIFICATION OF AMPHIBIA. 



605 



of that transition from aquatic to aerial respiration which 

 must have marked one of the most momentous epochs in 

 the evolution of Vertebrates. 



FIG. 327. Life history of a frog. After Brehm. 



1-3, Developing ova; 4, newly hatched forms hanging to water- 

 weeds ; 5, 6, stages with external gills ; 7-10, tadpoles during 

 emergence of limbs ; n, tadpoles with both pairs of limbs appa- 

 rent ; 12, metamorphosis to frog. 



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 Discoglossidae. 



Sub-order Phaneroglossa. Tongue present; the Eustachian tubes 



open separately into the pharynx. 



Series A. Arcifera (see p. 584), 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 (see p. 584), the frogs proper (Ranid^e), 

 e.g. the grass-frog (R. temporaria\ the edible 

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

 {R. catesbiana). 



