The integumental histology of Taricha granulosa (Skilton) has
been investigated with special attention being given to the seasonal
variations associated with terrestrial and aquatic habitats.
The epidermis consists of a stratified squamous epithelium,
four to seven cell layers thick, with one to two layers being cornified.
The dermis is composed of two layers. The outer stratum
spongiosum contains chromatophores, capillaries, smooth muscle
cells, fibroblasts and skin glands. The inner stratum compactum
is composed of horizontal bundles of collagenous fibers. The
granular and mucous glands are simple alveolar glands possessing
an intercalary region and a duct. The alveolar wall of the granular
gland is comprised of a columnar epithelium, muscle layer, and
connective tissue sheath. The mucous gland alveolar wall consists
of two layers, a cuboidal to columnar epithelium and a connective
tissue sheath.
The roughness of the terrestrial skin is due to two types of
tubercles. Major tubercles are caused by thickening of the epidermis
over a dermal papilla, while minor tubercles are merely thickenings
of the epidermis.
The aquatic epidermis is less cornified than that of the terrestrial.
It also shows a slight increase in height, which is particularly
evident in the tail. The swelling of the body and the enlarged
tail of the male in the aquatic stage are caused by an edema of the
stratum spongiosum. This stage also shows an increase in sub-epidermal capillaries and an increase in the activity of the mucous
glands. Both aquatic and terrestrial animals have granular glands
of equal secretory activity.
The aquatic phase possesses fewer glands per unit area of
skin due to the increase in the size of the dermis. Terrestrial newts
have the smallest granular glands and aquatic newts the largest,
though there is a strong overlap of granular gland volume in the two
stages. The aquatic phase has the largest mucous glands
