The Hexacanth Embryo of a Dilepidid Tapeworm. III. The Formation of Shell and Inner Capsule around the Oncosphere

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Abstract
The mature oncosphere was enclosed by 3 basic layers or egg envelopes. (1) The external shell capsule was formed from vitelline cell products and was not completed until late in development in the most gravid proglottids. This shell'' gave positive reactions for sclerotin. (2) A sub-shell colloidal envelope developed after the oncosphere became mature. This layer had metachromatic properties and formed a further barrier to diffusion. (3) An inner capsule appeared around the early oncosphere. It developed in association with certain macromeres and secretory products, and became a thick, rigid membrane. Changes in chemical nature of these envelopes was shown by changes in their affinity for certain counterstains. Schiff-positive substances increased during development in the region between the shell and oncosphere.