Abstract
AbstractThe spinal cord and the acoustic primordium of the chick embryo (3 to 7‐day‐old) were investigated by electron microscopy. Special attention was devoted to the structure of neurofilaments and tubules in the neuroblasts and cells of the crista acustica.The neurofilaments were observed to be related at early stages of development to the RNA particles of the cytoplasm (Palade's particles). This relationship is observed in particular fields which are clearly distinguished because they show fewer particles than the surrounding cytoplasm. The first stage is characterized by the presence in these fields of short branched filaments, which frequently are in contact with the ribosomes. The filaments grow in length and become ordered during a later period. At the same time, the fields become free of the basophilic particles.Tubules about 300 Å thick were found in neuroblasts and their prolongations (central nervous system); in the acoustic nerve, fibers of the “tubule type” or of the “neurofilament type” are described. Filaments and tubules showing similar morphology were also observed in the acoustic epithelium (crista acustica). The filaments seem to originate in the same way as in the neuroblasts. A close relationship between tubules and centrioles was found. The origin of the neurofilaments is discussed in relation to the filaments of proteinic nature described in other cell types.
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