A CYTOCHEMICAL INVESTIGATION OF OÖGENESIS AND DEVELOPMENT TO THE SWIMMING LARVAL STAGE IN THE CHITON, CHITON TUBERCULATUM L

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Abstract
Oocyte development in Chiton tuberculatum may be divided into 3 distinct stages. The initial stage was concerned with ribonucleoprotein synthesis; the cytoplasm was strongly basophilic and the nuclei contained a large basophilic nucleolus. In the intermediate stage, protein yolk was elaborated and levels of the cytoplasmic and nucleolar basophilia were reduced. The protein yolk granules were deeply stained by the PAS reaction, and by a protein tryptophan method. In the final stage, the cytoplasm was packed with protein yolk granules of uniform diameter; cytoplasmic basophilia was much reduced and the nucleoli were absent. A chorion and ornate chorionic processes were formed during the intermediate stage, probably by an interaction between the oocyte accessory cells and the oocyte. During subsequent development, the concentration of basophilic material (presumably RNA) and protein yolk was about the same in cleavage blastomeres of all sizes. Up to the swimming larval stage, only the prototroch and apical tuft exhibited the usual manifestations of RNA synthesis; i.e., the appearance of nucleoli and accumulations of cytoplasmic RNAase removable basophilia.

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