The bone of advanced teleost fishes such as those of the family Sparidae is said to lack osteocytes or to be acellular. Acellularity has been determined by apparent lack of osteocyte lacunae. This study questions the validity of this criterion. Scanning electron and light microscopy of paraffin and resin sections were used to show that the sides of sea bream mandibles consist of laminar parallel-fibred bone that we call tubular bone, because it contains tubules, and localised regions of Sharpey fibre bone. Osteocytes lie along the walls of tubules that also contain collagen fibril bundles (T-fibres), or in the lumens of tubules that do not contain T-fibres. We show that the osteocytes are derived from osteoblasts. The T-fibre system is different from other fibre systems that have been described. The tubules enclose wide T-fibres (lenticular in cross-section, maximum width about 8 microns) that taper at their ends and continue as thin T-fibres (round in cross-section, about 2 microns wide). The T-fibres originate in the periosteum. In mature tubular bone, spaces of increasing size develop around the osteocytes. Osteocytes are released from the bone matrix and become postosteocytes or bone-lining cells. Secondary bone lines the largest spaces. In Sharpey fibre bone, small osteocytes in small lacunae (about 2 microns wide) are found in columns parallel to the Sharpey fibres. Large osteocytes are found in large round spaces and are much larger than comparable osteocytes in lacunae in the bone of the salmon Salmo salar. We conclude that an absence of visible or conventional osteocyte lacunae does not mean that the cells themselves are absent. There are cells and two types of collagen fibre bundle in the tubules. The cells are osteocytes derived from osteoblasts, and these osteocytes apparently resorb bone with the result that large amounts of bone are destroyed. "Acellular" tubular and Sharpey fibre bone are types of cellular bone that differ from each other and from conventional cellular bone.

Scanning electron and light microscopy were used to show that the pedicels of fish teeth (the so-called "bones of attachment") consist of three types of dentine that lie concentrically around a pulp cavity lined with typical odontoblasts with cytoplasmic processes in dentinal tubules. Circumpulpal canalar dentine forms on a thin layer of orthodentine that is encased in mantle dentine. Canalar dentine is a new name given to a dentine that is similar to vasodentine in canal arrangement, but not apparently in canal content. An inner series of wide, radial canals and an outer series of highly-branched thin canals of two diameters are inhabited by a population of cells, the osteodentocytes, and collagen fibril bundles. The flat, oval osteodentocytes appear to be quiescent cells, lying on the sides of the tubules and covered by a sheath. Plump, intensely metachromatic osteodentocytes appear to be more synthetically active. The canals and the osteodentocytes originate from blood capillaries enclosed in the predentine during dentinogenesis. New teeth begin within the small cavities present in spongy bone that were enlarged by multinucleated osteoclasts during tooth growth. Pedicel formation is initiated by the extension of the crown mantle dentine, forming the outer layer of the crimped ligament and outlining the future length and curvature of the pedicel. Central and inner ligament zones are subsequently formed as orthodentine is secreted in both crown and pedicel, and canalar dentine in the pedicel. Spongy bone osteogenesis begins during stage 1 of pedicel formation with the aggregation of osteoblasts and blood capillaries in the bone cavities and in the dermis between the pedicels. Loose fibrillar osteoid condenses into incomplete thin trabeculae bordered by intensely metachromatic osteoblasts. Osteoblasts become enclosed in the developing trabeculae that thicken to give mature spongy bone with osteocytes throughout. We conclude that the pedicels are the true bases of teeth, that the dental ridge is formed from pedicels and spongy bone, and that sea bream spongy bone is cellular. The term "bone of attachment" is inappropriate for the pedicel. It can be used for the spongy bone between the compact bone of the jaw and between adjacent pedicel.

Many studies have been made on autotomy and regeneration of the tail in lizards; for example those by Woodland (1920) and Hughes & New (1959) on geckos, by Slotopolsky (1922) on Lacerta, by Barber (1944) and Kamrin & Singer (1955) on Anolis, and by Simpson (1964) on Lygosoma. This work is concerned with the adult, and, so far as we are aware, no comparable studies on young and embryonic lizards have been made. Indeed, the application of experimental techniques to reptilian embryology is still in its infancy (see Holder & Bellairs, 1962, 1963). In 1956 Panigel found that embryos of the common lizard (Lacerta vivipara) would develop, sometimes until hatching, when removed from the mother and kept under sterile moist conditions in a form of culture. Their yolk is sufficient for nourishment, and the rudimentary type of allanto-placenta which he describes seems to have no significant nutritive function.