imate knowledge of their generic characters, into a large number of
Genera; but all the Genera of Woodpeckers and all the Genera of the
Parrots are still held together by their form as Families, corresponding
as such to the two old Genera of _Picus_ and _Psittacus_. They are now
known as the Families of Woodpeckers and Parrots; and though each group
includes a number of Genera combined upon a variety of details in the
finish of special parts of the structure, such as the number of toes,
the peculiarities of the bill, etc., it is impossible to overlook the
peculiar form which is characteristic of each. No one who is familiar
with the outline of the Parrot will fail to recognize any member of
that Family by a general form which is equally common to the diminutive
Nonpareil, the gorgeous Ara, and the high-crested Cockatoo. Neither will
any one, who has ever observed the small head, the straight bill, the
flat back, and stiff tail of the Woodpecker, hesitate to identify the
family form in any of the numerous Genera into which this group is now
divided. The family characters are even more invariable than the generic
ones; for there are Woodpeckers which, instead of the four toes, two
turning forward and two backward, which form an essential generic
character, have three toes only, while the family form is always
maintained, whatever variations there may be in the characters of the
more limited groups it includes.

The Turtles and Terrapins form another good illustration of family
characters. They constitute together a natural Order, but are
distinguished from each other as two Families very distinct in general
form and outline. Among Fishes I may mention the Family of Pickerels,
with their flat, long snout, and slender, almost cylindrical body, as
contrasted with the plump, compressed body and tapering tail of the
Trout Family. Or compare, among Insects, the Hawk-Moths with the Diurnal
Butterfly, or with the so-called Miller,--or, among Crustacea, the
common Crab with the Sea-Spider, or the Lobsters with the Shrimps,--or,
among Worms, the Leeches with the Earth-Worms,--or, among Mollusks,
the Squids with the Cuttle-Fishes, or the Snails with the Slugs, or the
Periwinkles with the Limpets and Conchs, or the Clam with the so-called
Venus, or the Oyster with the Mother-of-Pearl shell,--everywhere,
throughout the Animal Kingdom, difference of form points at difference
of Families.

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