We have examined the fine structure of injured, repairing and regenerating tissues of the amputated forelimbs of the adult newt: observations were made on wound epithelium, nerves, striated muscle, the regeneration blastema, connective tissues and cartilage.The wound epithelium shows little modulation from the adjacent epidermis: a subjacent glycocalyx and hemidesmosomes are initially absent. Some cells reveal phagocytic activity. As regeneration progresses, a glycocalyx, hemidesmosomes, and a n adepidermal reticulum of fibers develop.Nerve fiber degeneration and regeneration lie side by side in the same nerve bundle. Myelin degeneration is evident within 24 hours; neural connective tissues loosen and fibers appear to spread apart.Striated muscle fibers display a nonuniform response to trauma, due to unequal degree of injury inflicted by amputation. The moderately and greatly injured fibess lose their distal fibril organization. There is a numerical increase i n mitochondria, and occasionally a pyknotic nucleus is present. The myofiber glycocalyx appears to resist destruction, even when cell degeneration is extensive. Satellite cells have been observed intimately in contact with injured myofibers. Myogenesis is accompanied by a n increase i n collagen fibrillogenesis associated with adjacent fibroblasts. Many of these latter cells appear to contain intracellular fibrils: the significance of these abservations are discussed, and a basis for intracellular fibrillogenesis and tropocollagen accretion is proposed.The fine structure of the regeneration blastema cell agrees with the description offered by others for the adult newt limb regeneration.Early prochondral condensation of blastema cells is described briefly.The amputated forelimb of the adult newt, Diemictylus viridescens regenerates and, i n doing so, exhibits the biological processes of inflammation, cell and tissue modulation, blastema development, growth, and differentiation (see Schmidt, '66 for review). The composite of these biological activities is a new limb that replaces the lost appendage.Regeneration as a whole is the result of cooperation among several heterogeneous processes on a temporal basis, and phases may be distinguished that lend themselves to individual investigation. A preblastemic phase includes wound-closure and healing of the amputee. This is followed successively by a blastema phase, and then a differentiative and morphogenetic phase leading to a reconstituted limb. Of these phases, the formation of the blastema, beginning in the preblastemic phase from among the injured limb tissues, and the J. MORPH., 123: 271-312.growth of the blastema itself are absolute prerequisites for regeneration. Therefore, much of our attention has been devoted to the fine structure of injured tissues and cells of the preblastemic, and blastemic phases; the differentiating tissues were selectively investigated.
MATERIALS AND METHODSThe adult newts, Diemictylus viridescens, obtained from the vicinity of Petersham, Massachusetts, were prepared for th...
