106 . 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 Cacilians 
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 Ce- 
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 
Naked Reptiles. The external likeness between 
these two groups is perhaps less striking than 
