(Cosenza) (Italy) MATERIAL AND METHODS Adult male specimens of Caiman crocodylus were captured in the State of Para, Brazil, Some small blocks of a testis were fixed by triple fixation (Sugihara et al., 1966). Other blocks were fixed in 31 glutaraldehyde in 0.1 M phosphate buffer, pH 7.2 and then in \l OsO 4 in the same buffer. After fixation, the blocks were dehydrated in ethanol, block-stained with uranyl-acetate, passed in propylene oxide and embedded in Epon-Araldite. Thin sections, stained with lead citrate, were examined with an Hitachi HU-12A electron microscope.

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The ultrastructure of perichondrial tissue of cartilage rudiments (metatarsus, tibiotarsus and sternum) of the chick embryo at various stages of development (H.H. stages 28-45) was investigated by transmission electron microscopy. Previous microscopic and submicroscopic data were generally confirmed, but new findings indicated: (a) the existence of a temporary syncytial state of perichondroblasts during the earliest developmental stages, (b) the existence of a perichondrial cambial layer of stem cells, (c) involvement of perichondroblasts in the appositional growth of cartilage. Electron microscopy revealed clear temporal relations between cell differentiation, perichondrial growth and the structure and production of perichondrial ECM. In addition, the boundaries between cartilage and perichondrial tissue were demonstrated unambiguously. Perichondrial structure varied specifically with each cartilage segment; in particular the perichondrium in long bone rudiments (where ossification starts early) contrasted with that in the permanent cartilage medial process of the sternum.

We studied structure and ultrastructure of the subepidermal connective tissue (SEC) of the integument of three cephalopods (Sepia officinalis, Octopus vulgaris and Loligo pealii). In all species, three distinct regions of the SEC were recognised: (a) an outer zone (OZ) that included the dermal-epidermal junction, and consisted of a thin layer of connective tissue containing muscles, (b) an extensive middle zone (MZ) containing a compact network of collagen fibres and numerous cells, (c) an inner zone (IZ) of loose connective tissue that merged with muscular fascia. This arrangement differs from that in bivalves and gastropods and recalls vertebrate integument. The dermal-epidermal junction of cephalopods differed from that of bivalves, gastropods and mammals in that the epidermal cells did not possess hemidesmosomes, and their intermediate filaments terminated directly in the plasmamembrane. The thick (120-500 nm) basal membrane (BM) had a superficial zone containing a regular array of granules; a lamina densa composed of a compact network of small filaments and granules; and an IZ distinguished by expansions of granular material protruding into underlying structures. Collagen fibres contained fibroblast-derived cytoplasmic thread, running through their centres and were surrounded by granular material that joins them to adjacent fibres. The collagen fibrils were of medium diameter (30-80 nm) had the typical ultrastructure of fibrillar collagens, and were surrounded by abundant interfibrillar material. The hypodermis was loose, with a network of small bundles of collagen fibrils. Cephalopod integument appears to represent a major evolutionary step distinguishing this class of molluscs.

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