CHAPTER XI 

 AMPHIBIA (BATRACHIA) 



As the name indicates this is a class of animals that have two modes 

 of life, aquatic and terrestrial. The eggs are usually laid in water and 

 hatch into fish-like tadpoles that may later give up their aquatic habits 

 and live on land. Nearly all of them breathe by gills, in the larval 

 condition, and many of them retain these gills through life, though lungs 

 are usually present in the adult, sometimes being present in the same 

 animal with the gills. The Amphibia, though so fish-like in many cases, 

 are distinguished from the Pisces, by having pentadactyle limbs, usually 

 without claws, in place of paired fins (where paired appendages are 

 present at all) and by the absence of fin-rays in the median fins, where 

 these organs are present. The skin is glandular and a bony dermal 

 exoskeleton is sometimes present. There are also numerous character- 

 istics of internal structures that need not be noted here. 



The Amphibia are interesting as illustrating the transition from 

 water-breathing to air-breathing forms. The lower species retain their 

 gills throughout life, while the higher forms lose their larval gills and 

 breathe entirely by means of their lungs and skin. This metamor- 

 phosis from the tadpole to the adult may take place in a few months or 

 it may take a much longer time. Coincident with the disappearance of 

 the gills and the development of the lungs the limbs usually make their 

 appearance, the tail is absorbed, and other marked external and inter- 

 nal changes take place, Fig. 86. 



As noted later, the tailed amphibia are very commonly confused 

 with certain reptiles and called lizards; but they may usually at once 

 be distinguished from the latter by the absence of scales and claws and 

 by differences of habits, the former being usually found in dark, moist 

 places while the latter prefer dry, sunny localities. 



There are fewer known species of living Amphibia than of any of the 

 vertebrate classes, the estimates varying from about noo to 2200. 

 With the, extinct forms we are not especially concerned since they can 



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