In the eye of Squilla mantis adapted to the dark the layer of the crystalline cones shortens and the retina becomes longer; the opposite occurs in light adaptation. With dark adaptation the acceptance angle becomes more than twice as large as in light adaptation. With this also the visual field of the ommatidium and the gaussian sensitivity function increase. Myofibrils between the crystalline cones are immersed in veils which are attached to the cornea. At the widest part of the cone a reinforced cone membrane folds inside; the fold contains a ring to which the veils are attached. This unique structure serves possibly as a harness to transfer the mechanical traction of the contractile structures to the cone. Around the distal, tapering part of the cone, the corneagenous cells could act as hydraulic shock-absorbing cushions. Six accessory pigment cells stretch between the distal retina and the basement membrane and contain myofibrils. The shortening of the cones during dark adaptation is presumably due to the contraction of the myofibrils in the veils and the simultaneous relaxation of those in the accessory pigment cells. In light adaptation the latter contract and the fibers in the veils relax.
The annual reproductive cycle was studied in a Triturus alpestris apuanus population from northwestern Italy. Adult and larval newts were captured and measured monthly. By using histological techniques, the status and evolution of male gonads were examined. T. a. apuanus shows a post-nuptial gametogenesis, and testes reach their smallest size and weight in spring, when there are mainly mature sperm ampullae and yellow glandular tissue. Secondary sexual characters reach their maximum development during this period, decreasing during gametogenesis and increasing again in early autumn. Breeding activity begins at the same time, and is interrupted by the winter. Reproduction starts again in spring, lasting until summer. Eggs are laid at least twice a year, and the two larval cohorts live together. It is suggested that all these biological features are adaptations to unpredictable aquatic environments in a Mediterranean dry climate. These results suggest high levels of flexibility and variability in newt seasonal cycles.
Microscopy and histology techniques can be applied to morphological study of fungi and bacteria contaminating ancient human osteological remains. Undecalcified samples are cut with a diamond rotary blade microtome and an original technique was applied using adhesive tape to prevent damage to the bone surface during sectioning. We used light microscopy, polarized light microscopy, and epi-illumination fluorescence systems. Common dyes can be applied to 80 microm sections using classic staining techniques to reveal the architecture of bone and the presence of infecting biological agents.
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