Normal development of the Ambystoma mexicanum skull was compared with those in axolotls reared at different TH concentrations and in the TH-deficiency. Cranial bones show different TH-dependence. The latter is at best low (if ever) in the early-appearing bones; it somewhat increases in later ones and becomes strong in the nasal and septomaxilla, the last dermal bones to arise. Bones appearing after this peak TH-dependency revert back to be TH-independent. Similar ontogenetic dynamics of TH-dependency is displayed by metamorphosing urodeles. Axolotls retain this typical pattern though their plasma TH level and TH profile differ from those in metamorphosing salamanders. However, if compared with metamorphosing congenerics, changes in the thyroid activity (manifested as changes in TH level and profile) cause changes in the timing and sequence of cranial ossification. To be normally developed, dermal bones associated with nasal capsule require the presence of the underlying cartilage. Their underdevelopment in axolotl results from the underdevelopment of the TH-dependent nasal capsule rather than immediately from TH-deficiency. Our observations favor the assumption that urodele evolution is accompanied by the progressive increase of TH-mediation in the skull ontogeny. Also, they favor that formation of the vomeropalatine in TH-induced axolotls is artifact of TH-induction rather than a feature of their normal development.

The first morphological and ultrastructural description of testis, Wolffian duct, spermatophore, and spermatozoon of Lissotriton italicus is provided. The male reproductive system of this species consists of a pair of monolobed testes, fat bodies, efferent ductules, paired Wolffian duct, and the cloaca. The Wolffian duct is pseudostratified, consisting of an epithelium composed of an alternation of ciliated cells and non-ciliated secretory cells, with scattered basal cells. Melanocytes are found in the basal lamina of the Wolffian duct. Spermiogenesis is of the discontinuous type. In the early spermatid nuclear elongation, flagellar extrusion and development of a large acrosomal vesicle occur. Soon the perforatorium develops and the flagellum elongates. In the late spermatid gradual chromatin condensation and nuclear elongation is noticeable. At the end of spermiogenesis the flagellum develops marginal filament and undulating membrane. The mature sperm of L. italicus consists of a distinct head (acrosome, perforatorium, nucleus and nuclear ridge, plus the apical acrosomal barb) and a tail with axoneme, undulating membrane, and axial fiber. Nuclear ridge and apical acrosomal barb are two autapomorphic characters found in the Urodela. Several apomorphic characters for Salamandroidea are also present: elongation of the connecting piece, an apically modified acrosome vesicle, trifoliate axial fiber within the principal piece, elongate annulus, elongate midpiece, and the gentle merging of the axial fiber/principal piece into the endpiece. The spermatophore of L. italicus is formed by a cap consisting of randomly distributed spermatozoa surmounting a short pedicel. A membranelike structure involving the spermatophore is absent.

By using immunohistochemical techniques applied to confocal microscopy, the presence of aquaporin 3 water channel in the epidermis of Triturus italicus (Amphibia, Urodela) has been shown. We analysed the expression of aquaporin 3 (AQP3) during the larval, pre-metamorphic and adult phases; we also showed the localization of the water-channel protein AQP3 in free-swimming conditions and during aestivation in parallel with histological analysis of the skin, focusing on the possible relationship between protein expression and terrestrial habitats. Our results indicate that aquaporin is produced as the epidermis modifies during the functional maturation phase starting at the climax. Moreover, our data suggest an increase in enzyme expression in aestivating newts emphasizing the putative functional importance of differential expression related to a distinct phase of the biological cycle.

Balancer morphology and ultrastructure, with emphasis on changes occurring during development, are described for Triturus italicus, using stereomicroscopy and light microscopy, as well as scanning and transmission electron microscopy. Morphological differentiation of balancers involves elongation, swelling of the distal region of the organ and appearance of secretory cones. The extensive granular endoplasmic reticulum and the well-developed Golgi apparatus characterize the inner cell layer of the mature balancer. Other characteristics include the presence of numerous rounded lipid-like granules and extensive innervation. In the cytoplasm, numerous bundles of tonofilaments can be found, and their amount increases as development progresses. As already stated in previous studies, the general morphology of balancers shows great constancy.