VERTEBRATA (CHORDATA). 



93 



The genus Siredon (Axolotl), if regarded as a permanent type, must be 

 placed, as above, among the Perennibranchiate Urodela. It has been 

 shown, however, by Dumeril, Marsh, and others, thafc under certain cir- 

 cumstances the Axolotl may lose its gills, and may undergo other changes, 

 by which it becomes an Amblystoma. There would, therefore, be no im- 

 propriety in regarding the ordinary Axolotls as persistent larvae, and in 

 placing the genus Siredon among the Amblystomidce. 



Fig. 83. Ophiomorpha. a, SipTionops annulatus, one of the Cseeilians, much reduced ; 6, 

 Head ; c, Mouth, showing the tongue, teeth, and internal openings of the nostrils ; d, Tail 

 and cloacal aperture. (After Dumeril and Bibron.) 



Fig. 84. Tailed Amphibians. A, Siren lacertina ; B, Amphiuma, showing the four 

 minute limbs ; c, Menobranchus maculatuis. (After Mivart.) 



