Vertebrata. 



FIG. 



wasting and disappearing on the development of the 

 lungs. Of the former, we perennibranchiate section we 

 have interesting examples in the sirens or mud .eels of 



Carolina, which are 

 provided with only 

 two limbs represent- 

 ing the fore limbs 

 of other verte- 

 brates. Another 

 form, the proteus, 

 inhabits the Cave 

 of Adelsberg and 

 other caves in Ca- 

 rinthia, &c., and is, 

 like all other cave- 

 dwellers, blind and 

 blanched ; its weak 

 fore legs are pro- 

 vided with three 

 toes, while the hind 

 limbs possess only 

 two. The curious 

 axolotl (fig. 1 6) of 

 Mexico is an inte- 

 resting form, as it 

 has proved to be a 

 permanent tadpole 

 which in certain 

 conditions only un- 

 dergoes its further metamorphosis into the salamander- 

 like form of its adult state. 



Jn some perennibranchs the outer gills disappear, 



Diagram of the axolotl, showing its gills, 6, 

 and lungs, v. 



