Development of cutaneous glands in Salamandrina terdigitata (Lacépède, 1788) (Amphibia: Urodela); findings by light and electron microscopy.

Cutaneous glandular Anlagen in Salamandrina terdigitata appear in the early larval stages as sphere-shaped intraepidermal cell nests. A stromal screen rises into the epidermis from the primordial dermis surrounding the Anlagen and isolates them from future keratinous elements. At this stage the only contact between the stroma and the gland blastocytes is through their cell coat, whilst the adjacent keratinocytes show a complex dermo-epidermal type junction. This structural asymmetry, confirmed by cytochemical findings, plays a direct role in guiding processes governing glandular bud differentiation. Interactions are in fact established between the stroma and the ample portion of the Anlage which it surrounds, which coordinate development, initiating differentiation of the contractile and secretory elements. Only a few bud cells, grouped below the epidermal basal layer, avoid such contact with the dermis, and constitute the regenerative matrix of the gland by maintaining their indifferentiated state. Above these, several keratinocytes form the excretory duct.