The presence and distribution of glycogen particles in chondrogenic cells of the tibiotarsal anlage of developing chick embryos.

The distribution and localization of glycogen particles in mesenchymal cells, chondroblasts and in young, hypertrophic and degenerating chondrocytes of the tibiotarsal anlage of developing chick embryos were examined ultrastructurally using the periodic acid--thiocarbohydrazide--silver proteinate. The distribution of glycogen particles increased with the degree of differentiation and maturation of the chondrogenic cells. Mesenchymal cells showed minimal content of glycogen particles which gradually increased in the chondroblasts. The young chondrocytes further showed increased glycogen particle content compared to chondroblasts. This content reached a maximum level in hypertrophic chondrocytes. This level subsided in degenerating chondrocytes which showed a much reduced distribution of glycogen particles compared to hypertrophic chondrocytes. The morphological nature of glycogen particles depended on the degree of cellular differentiation. Both mesenchymal cells and chondroblasts contained single particles, while the glycogen particles of chondrocytes aggregated and formed a series of interconnected particles.