The Hexacanth Embryo of a Dilepidid Tapeworm I. The Development of Hooks and Contractile Parenchyma

Abstract

The morula of Dilepis undula (Schrank). developed in the strobila as the result of cleavage, became an hexacanth embryo (oncosphere) by developing muscular parenchyma, hooks, cuticle and epidermal glands. Hooks developed in oncoblasts. First the blade was formed, then the shank. Three morphologically different pairs of hooks were made dorsal-lateral, ventral-lateral and medial. Hooks were protein in reaction. Differentiation of parenchyma in the oncosphere occurred by the transformation of embryonic mesenchyme cells. Nuclei tended to become pyenotic and a contractile stroma was formed. Cortical and medullary contractile systems that move hooks and body of oncosphere are described. The cortical system, derived from the cortical parenchyma, was considered homologous with the subcuticular musculature of the metacestode stage. The medullary system, derived from a binucleate contractile center, was considered homologous with the longitudinal musculature of the metacestode.