2-44 FROGS, TOADS, AND SALAMANDERS 



breathing animals. The lower of the amphibians — the 

 necturus and the siren — [jass their entire lives in the water 

 and possess gills in the adult stages. The higher amphibians 

 — toads and frogs — live on land in the adult stage, and 

 possess luirgs. 



Among the so-called salamanders, there is, at least, one 

 species that, within its own lifetime, may pass in transition 

 from the lower to the higher types of the Amphibia. That 

 is, the indivi{.luals of this particular species of salamander 

 may, under stress of circumstances, change from a form that 

 possesses external gills and is fitted for an acjuatic life to a 

 form that p(jssesses lungs and is fitted for life on land. In 

 either of these stages, this amphibian, the axolotl, breeds 

 successfully and reproduces its kind. When in the aquatic 

 form, the axolotl has the structure, habits, and habitat of 

 the lower ampliil)ians; ])ut when it assumes the land form, 

 it has the structure, habits, and habitats of the higher 

 amphibians. Tliis remarkable twofold life is evidently an 

 adaptation to the environment of this animal. When the 

 ponds in whicli it lives are about to dry up, it assumes 

 the land form, and in this stage it has long been known as 

 the spotted salamander. 



Economic importance of the Amphibia. — As a group, 

 the Amphi])ia are not of great economic importance, for 

 there are only two species that are considered to possess 

 any significant economic value, namely, the bullfrog and the 

 toad. The bullfrog may be found in season in the markets 

 of all of our lar'ge cities. In France and in southerir Europe, 

 the European green frog is reared in "froggeries" and used 

 extensively as an article of food. Fi'om a juii-ely agi'arian 

 |)(iiiit of view the common toad has a greater economic 

 value th;an any other amphibian. 



