CIIOKDATA 





attain a length of nearly two meters, and just before the dry 

 season buries itself in the mud, where it remains coiled up and 

 quiescent until the return of moisture. The remains of fossil 

 Dipnoi are abundant in Europe and America. These fishes are 

 of considerable importance, as they are believed to form a con- 

 necting link between the lower fishes and the next class of vcrte- 

 brata to be considered, the Amphibia. 



CLASS III. AMPHIBIA 



The Amphibia (Gr. afx(j>i, both, and /3<o9, life) are familiar 

 through such representatives as the salamanders, frogs, and 

 toads. As a rule they pass through a larval stage in the water, 

 and in the adult condition may live upon land, although mam- 

 remain in the water all their lives. They are found in fresh 

 water, never in salt. The body is covered with a soft, naked 

 skin, except in one group, which possesses minute scales, but 

 some of the extinct Amphibia were provided with well-developed 

 bon)- plates in the integument. Some extinct species were 

 gigantic in size ; in one the skull alone was over a meter and a 

 half long. The skin contains numerous glands, which by their 

 secretions keep it moist while out of the water. In some species 

 the secretion is poisonous to other animals. The outer layer of 

 the skin is shed periodicallv. 



Many Amphibia which possess tails, such as the hellbender 

 and mud puppy of our Central states, are strikingly fishlike in 

 appearance. There is an unpaired fin on the dorsal side, con- 

 tinuing about the diphycercal tail and along the 'posterior part 

 of the ventral side, like the median fin of the 'Dipnoi, the true 

 eels, and some other fishes. But this fin is never provided with 

 skeletal supports, or fin-rays, as in the fishes. The great differ- 

 ence externally between such Amphibia and the fishes is found 

 in the paired appendages, which here are never fins, but penta- 

 dactyl extremities, or legs. As a rule there are two pairs of 

 these, anterior and posterior, or pectoral and pelvic ; but in a 

 tew cases only the anterior pair is present, and in a tew both 

 pairs are absent. These appendages are provided with an in- 

 ternal bony skeleton, and the arrangement of the bones is on 

 the same plan in this and all the higher groups of Vertebrata ; 



