Most adults and a few juveniles examined in the field and laboratory
had one or more small injuries on the carapace that had healed or were
undergoing repair. Such injuries almost never occurred on the
plastron. In an injury that was undergoing repair, a small piece of
smooth, whitened bone was exposed where a piece of epidermis was
missing from the shell. One or more edges of the exposed bone
characteristically projected over the surrounding epidermis, making
the bone appear as though it had been driven forcefully, like a
splinter, into the shell (Pl. 29, Figs. 1 and 2). Because of their
curious appearance, small areas of repair were referred to in my notes
as "splinter scars." The position and number of splinter scars were
often recorded as supplementary means of individualizing turtles in
the field.
Splinter scars result from minor abrasions that damage a few square
millimeters of the shell. Larger areas of exposed bone were noted in
only a few specimens. Two turtles at the Damm Farm had bone exposed on
more than one-half the surface area of the carapace; both of these
turtles were probably burned in the grass fire of 1955. Ordinarily, a
break in the shell does not induce extensive regeneration of tissues;
when shells are damaged by crushing or cracking, regeneration of
epidermis and bone occurs only along the lines of fracture, unless the
broken parts have been dislocated. Ligamentous tissue develops in some
breaks on the plastron, the broken area remaining slightly movable
after healing is completed (Pl. 24).
Dissection of injured shells revealed the mode of shell regeneration
to be the same whether a large or small portion of the shell had been
damaged. An abrasion may gouge out a small portion of the shell;
burning, freezing, or concussion may kill a portion of the epidermis
and a corresponding portion of bone beneath it without actually
disfiguring the shell. Dead bone and epidermis become loosened at the
margin of the wound. The epidermis sloughs off soon afterward but the
bone adheres to the wound. New epidermis and new bone, growing from
undamaged tissues at the edges of the wound, encroach on the wound
beneath the layer of dead bone. The piece of dead bone is thereby
gradually isolated from the rest of the shell and is sloughed off when
healing is complete. The dead bone may come off in one piece or slough
off gradually at its edges as healing proceeds toward the center of
the wound. The layer of dead bone protects the wound during the
process of regeneration (Pl. 30). Areas of exposed bone become white
and shiny, nearly enamellike in appearance, as a result of wear on the
shell.
The above conclusions, in regard to _T. ornata_, agree basically with
the findings of Woodbury and Hardy (1948:161-162) and Miller
(1955:116) on regeneration of the shell in desert tortoises (_Gopherus
agassizi_). Danini (1946:592-4, English summary) made histological
studies on regeneration of the shell in specimens of _Emys
orbicularis_; he found that new bone trabeculae formed on the surfaces
of undamaged trabeculae at the edge of the wound and formed also in
connective tissue at the center of the wound. Regeneration of bone was
incomplete in some instances where total extirpation of a portion of
the shell had occurred. Regenerated epidermis was usually thicker than
the original scute.
Exposed bone on the shells of turtles that have been injured in fires,
although dead, is unmarked and shows no evidence of being burned.
Exposure to fire kills the growing portions of both the epidermis and
the bone but seemingly does not actually char or disfigure the bone
(although the epidermis may be so affected) (Pl. 29, Fig. 3). Injuries
from fire result probably from brief encounter with the fire itself or
from more prolonged contact with some surface heated by the fire. A
turtle that remained in a fire long enough to have its shell charred
would presumably have little chance of survival. Grossly disfigured
shells therefore do not result directly from burns but are due to the
gnarled texture of the regenerated bone and epidermis remaining after
the dead portions of the shell have been sloughed off. Information on
injuries from fire was supplemented by examination of several badly
burned specimens of _T. carolina_. Their shells were nearly covered
with exposed bone and regenerated epidermis. One specimen was so badly
damaged that the entire anterior rim of its carapace was loose and
could be pulled away easily to disclose a gnarled mass of regenerating
bone beneath it (Pl. 29, Fig. 3). There were areas near the posterior
margin of the carapace of each specimen where regenerated epidermis
was evident but where the bone was seemingly uninjured; the
regenerated epidermis was nearly transparent.
Areas of regenerated epidermis on specimens of _T. ornata_ were rough
in texture and slightly paler than the surrounding scutes.
Color-pattern is not reproduced in the process of regeneration but
irregularly shaped light blotches sometimes occur in the places where
radiations or other distinct markings formerly were present. A slight
depression remains on the shell after regeneration is completed. I
suspect that small injuries may be repaired in the course of a single
growing season but that injuries involving a large part of the shell
may take several years to heal completely. Cagle (1945:45) reported
that a bullet wound in the shell of a painted turtle (_Chrysemys
picta_) healed completely in approximately 23 months. Danini (_loc.
cit._) found that regeneration of the shell in _Emys orbicularis_ was
complete in as short a time as 225 days. Woodbury and Hardy (_loc.
cit._) stated that small injuries to the shell of _Gopherus agassizi_
may take as long as seven years to heal.