BRANCH CHORD AT A: CLASS B AT R A CHI A 297 



the spring- to lay their eggs. Most batrachians are very 

 tenacious of life, being able to withstand long periods of 

 fasting and serious mutilation, and most of them can 



t> 



regenerate certain lost parts, such as the tail or legs. 



Classification, The living Batrachia are divided into 

 three orders, viz., the Urodela, including the sirens, mud- 

 puppies, salamanders, and newts, batrachians which retain 

 the tail throughout life, having generally two pairs of limbs 

 of approximately equal size, and sometimes possessing 

 gills or gill-slits in the adult condition ; the Anura, or 

 frogs and toads, with no tail in the adult condition, with 

 short and broad trunk, with hind limbs greatly exceeding 

 the fore limbs in size, and never with gills or gill-slits 

 in the adult stage; and the Gymnphiona, or ccecilians, 

 snake-like batrachians having neither limbs nor tail, with 

 a dermal exoskeleton and without gills or gill-slits in the 

 adult. 



Mud-puppies, salamanders, etc. (Urodela). TECHNI- 

 CAL NOTE. If possible obtain specimens of mud-eels (Siren], com- 

 mon in the South, or mud-puppies (Necturus], common in the cen- 

 tral North, as examples of batrachians with gills persisting in the 

 adult stage. One or more species of Amblystoma may be found in 

 almost any part of the country, and larvae of large size may be found 

 with the external gills. For an example of the general long-tailed 

 or Urodelous type of batrachian any salamander or newt occurring 

 in the vicinity of the school may be used. The little green triton or 

 eft (Diemyctylus viridiscens} of the eastern States, or its larger 

 brown-backed congener of the Pacific coast (D. torosus] is common 

 in water, while another eft, the little red-backed salamander, 

 (Plethodon} is common in the woods under logs and stones. The 

 external characters of the body should be compared with those of 

 the toad. The skeleton should be prepared by macerating away 

 the flesh (for directions, see p. 452), and the presence of the many 

 caudal vertebrae and the ribs, the equality in size of the legs, and 

 other points should be noted. Compare with skeleton of toad. 

 Make drawings. It will be well, also, to dissect out and examine 

 the various internal organs of the salamander, comparing them with 

 the same organs in the toad. The salamander,, indeed, is in many 

 ways better than the toad as an example of the class. Its body is 

 less adaptively modified and shows the essentially fish-like charac- 

 ter of the batrachian structure. 



