CHORDATA — VERTEBRATA — AMPHIBIANS 353 



equal limbs are usually present. In some (as Necturus and 

 the eel-like Siren of North America) gills are present through- 

 out life; in others (as the salamanders and the American 

 Amblystoma) the adult breathes by means of lungs. 



Fossil remains are rare. They have been found from the 

 Jurassic to the present. A giant salamander from the Miocene 

 of Oeningen, Baden, was mistaken by the early scientist Scheuch- 

 zer for the remains of a man and named by him Homo diliivil 

 testis (man as witness of the flood) ; this famous fossil, now 

 named Andrias scheuchzeri, is preserved in the Teyler Museum 

 in Haarlem. 



Order j, Anura {Frogs, Toads) 



Tail absent in the adult (whence the name from Greek a, 

 implying negation, + oura, a tail). Hind limbs much larger 

 than fore. Gills never present in adult. 



The eggs of frogs (in shapeless masses) and toads (in ropes) 

 look like little black beads (the yolk) surrounded by transparent 

 jelly (the white). Each bead attracts the sun's rays, w^hich 

 causes the germ or fertilized cell within to develop, through feed- 

 ing upon the yolk and white, into the embryo young. In about 

 two weeks the embryo leaves what is left of the jelly. It then 

 has external gills ; but later internal gills develop from slit-like 

 openings in the gullet walls, and the external gills, always a 

 source of danger, are gradually resorbed. This tadpole is now 

 in the fish stage, in which respiration takes place by the water 

 passing in through the mouth and out through the openings in 

 the gullet walls over the gills. Next the fore and hind limbs 

 bud out and become jointed, lungs are formed, gills and tail 

 entirely disappear and the developing animal becomes adult 

 in appearance. 



Fossils are rare, and are known only from the Comanchean 

 to the present. These include remains of both frogs and toads. 



2A 



