212 



VEKTEBKATA: BATRACHIA OE BATRACHIAXS. 



external branch ias that occur in tufts, covering the bran- 

 chial orifices. They also have lungs like others of their 

 class, and are thus true amphibians. It will be observed 

 that, even in their adult state, these animal* represent the 

 embryonic forms of the higher hatrachians. They are one 

 to two feet in length iu most cases, and constitute the 

 family of Sirenidse. 



The Siredons or Axolotls of Mexico and of Western 

 North America are from six to ten inches long, and every 



Siredon, Siredon lichenoiclej, Baircl. 



way similar in form to young aquatic salamanders. They 

 live mainly in the water. Proteus, represented by a spe- 

 cies a foot long in the waters of Adelsberg Cave, Carniola, 

 is a related genus. 



The Siredons have always been regarded with great 

 interest, because they represent, even in their adult form, 

 one of the transient stages of the higher urodelan-batra- 

 chians. But, of late, they have become still more inter- 

 esting, from the fact that Prof. O. C. Marsh (see Am. 

 Join-, of Sci. and Arts, Nov., 1868) has discovered that, 

 under some circumstances, the Siredon lichenoides, Baird, 

 wholly abandons the Siredon form, and becomes a genuine 

 Amblystoma mavortium, Baird. Fig. 283 is a copy of 

 Marsh's figure of the Amblystoma after it had passed 

 through its entire transformation. 



