h
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 condition; 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 collateral types,--the Turtles at the head of the Scaly
Reptiles, the Toads and Frogs at the Lead of the Naked Reptiles. The
external likeness between these two groups is perhaps less striking than
between those mentioned above, on account of the large shield of the
Turtle. But there are Turtles with a soft covering, and there are some
Toads with a hard shield over the head and neck at least, and both
groups are alike distinguished by the shortness and breadth of the body
and by the greater development of the limbs as compared with the lower
Reptiles. But here again there is the same essential difference in the
mode of development of their young as distinguishes all the rest. The
two series may thus be contrasted:--

_Naked Reptiles_. Toads and Frogs, Salamanders, Caecilians.

_Scaly Reptiles._ Turtles, Lizards, Serpents.

Such corresponding groups or parallel types, united only by external
resemblance, and distinguished from each other by essential elements of
structure, exist among all animals, though they are less striking among
Birds on account of the uniformity of that class. Yet even there we may
trace such analogies,--as between the Palmate or Aquatic Birds, for
instance, and the Birds of Prey, or between the Frigate Bird and the
Kites. Among Fishes such analogies are very common, often suggesting a
comparison even with land animals, though on account of the scales and
spines of the former the likeness may not be easily traced. But the
common names used by the fishermen often indicate these resemblances,
--as, for instance, Sea-Vulture, Sea-Eagle, Cat-Fish, Flying-Fish,
Sea-Porcupine, Sea-Cow, Sea-Horse, and the like. In the branch of
Mollusks, also, the same superficial analogies are found. In the lowest
class of this division of the Animal Kingdom there is a group so similar
to the Polyps, that, until recently, they have been associated with
them,--the Bryozoa. They are very small animals, allied to the Clams by
the plan of their structure, but they have a resemblance to the Poly