L06 ANALOGOUS TYPES. 



contraction behind it, such as marks the neck in 

 the higher Reptiles, and moves only by the action 

 of the backbone ; they are singularly alike in 

 their external features, but the young of the Ser- 

 pent are hatched in a mature condition, while 

 the young of the type to which the Caecilians 

 belong undergo a succession of metamorphoses 

 before their resemblance to the parent is clearly 

 defined. Or compare the Lizard and the Sala- 

 mander, in which the likeness is perhaps even 

 more striking ; for any inexperienced observer 

 would mistake one for the other. Both are in 

 some respects superior to the Serpents and Cae- 

 cilians, for in them the head moves freely on the 

 neck, and they creep on short, imperfect legs. 

 But the Lizard is clothed with scales, while 

 the body of the Salamander is naked, and the 

 young of the former is complete when hatched, 

 while the Tadpole born from the Salamander has 

 a life of its own to live, with certain changes to 

 pass through before it assumes its mature con- 

 dition ; during the early part of its life it is even 

 destitute of legs, and has gills like the Fishes. 



Above the Lizards and Salamanders, highest 

 in the class of Reptiles, stand two other collat- 

 eral types, — the Turtles at the head of the Scaly 

 Reptiles, the Toads and Frogs at the head of the 

 Xaked Reptiles. The external likeness between 

 these two groups is perhaps less striking than 



