The markings of the shell change first when postnatal growth begins
and again when sexual maturity is attained. They are modified
gradually thereafter as the shell becomes worn.
In hatchlings the ground color ordinarily is dark brown but in some
individuals is paler brown or tan. Markings on the dark background are
pale yellow. Markings on the central and lateral scutes vary from a
regularly arranged series of well defined spots and a middorsal stripe
to a general scattering of small flecks. In some specimens the pale
markings of the carapace are faint or wanting. Lateral parts of
marginal scutes are always pale yellow and form a border around the
carapace.
Close examination of the carapace of any hatchling shows the following
basic arrangement of markings: each lateral scute has a centrally
placed pale spot and four to seven smaller pale marks arranged around
the edge of the scute; each central scute has a central, longitudinal
mark and several (usually two, four, or six) smaller pale marks
arranged around the edge of the scute, chiefly the lateral edges (Pl.
23). Variations in pattern result when some or all of the markings
divide into two or more parts.
By the end of the first full season of growth, the markings have a
radial pattern. At this stage, the markings of the areola, with the
exception of the central spot, are obscure. The radial marks, sharply
defined and straight-sided, appear only on the newly formed parts of
the epidermal laminae. Each radial mark originates opposite one of the
peripheral marks of the areola. Other radial marks are developed later
by bifurcation of the original radiations.
The ground color of the plastron of hatchlings is cream-yellow, or
less often, bright yellow. The solid, dark brown markings on the
medial part of each lamina form a central dark area that contrasts
sharply with the pale background (Pl. 24). The soft tissue of the
navel is pale yellow or cream; when the navel closes, the dark
central mark of the plastron is unbroken except for thin, pale lines
along the interlaminal seams.
When growth begins, the areas of newly formed epidermal tissue on the
anterior and medial borders of each areolar scute are pale. Wide, dark
radial marks, usually three per scute, appear on the newly formed
tissue. Subsequently, finer dark radiations appear between the three
original radiations. The wide radiations later bifurcate. By the time
adult or subadult size is reached, the plastron appears to have a
pattern of pale radiations on a _dark_ background. In general, the
markings of the plastron are less sharply defined than the markings of
the carapace (Pl. 24).
There is a tendency for the dark markings of the plastron to encroach
on the lighter markings, if no wear on the shell occurs. However, as
the plastron becomes worn, the pale areas become more extensive and
the dark markings become broken and rounded. Severely worn plastra of
some old individuals lack dark markings. Wear on the carapace produces
the same general effect; but markings of the carapace, although they
may become blotched, are never obliterated in _Terrapene o. ornata_.
The top of the head in most hatchlings is dark brown, approximately
the same shade as the ground color of the carapace; the part anterior
to the eyes is usually unmarked but a few individuals have a
semicircle of small pale spots over each eye or similar spots on much
of the head. The posterior part of the head is ordinarily flecked with
yellow. The skin on the top of the head, particularly between the
eyes, is roughened. The granular skin of the neck is grayish brown to
cream-yellow. There are one or two large pale spots behind the eye and
another pale spot at the corner of the mouth. Smaller, irregularly
arranged pale markings on the necks of some specimens form, with the
post-orbital and post-rictal spots, one or two short, ragged stripes.
The gular region is pale.
In juveniles, the yellow markings of the head and neck are larger and
contrast more sharply with the dark ground color than in hatchlings.
Markings above the eyes, if present, fuse to form two pale,
semicircular stripes. In some older juveniles yellow marks on top of
the head blend with the dark background to produce an amber color. The
top of the neck darkens or develops blotches of darker color that
produce a mottled effect. Spots and stripes on the side of the neck
remain well defined. The skin on top of the head becomes smooth and
shiny.
Adult females tend to retain the color and pattern of juveniles on the
head and neck although slight general darkening occurs with age. Many
adult females have the top of the head marked with bright yellow
spots. In adult males, the top and sides of the head, anterior to the
tympanum, are uniformly grayish green or bluish green; the mandibular
and maxillary beaks are brighter, yellowish green. Markings on the
head and neck of most adult males are obscure (Pl. 25) but the sides
of the neck remain mottled in some individuals.
The antebrachium has large imbricated scales and _is_ distinctly set
off from the proximal part of the foreleg which is covered with
granular skin. The antebrachial scales of hatchlings are pale yellow;
each scale is bordered with darker color. General darkening of the
antebrachium occurs at puberty. In adult females each scale on the
anterior surface of the antebrachium is dark brown and has a
contrasting yellow, amber, or pale orange center. The anterior
antebrachial scales of adult males are dark brown to nearly black and
have bright orange or red centers. Old males have thickened
antebrachial scales.
The iris of hatchlings and juveniles is flecked with yellow and brown;
the blending of these colors makes the eye appear yellow, golden, or
light brown when viewed without magnification. Adult females retain
the juvenal coloration of the eye; the iris of adult males is bright
orange or red. The work of Evans (1952) on _T. carolina_ suggests that
eye color in box turtles is under hormonal control.