Taenia crassiceps: ultrastructural observations on the oncosphere and associated structures.

Electron microscopic observations were made on unhatched eggs of Taenia crassiceps in utero. The outermost envelope consists of a thin, relatively smooth capsule over a highly convoluted outer envelope which contains a highly granulated cytoplasm and numerous mitochondria. The inner envelope, consisting of a thick embryophore and the cytoplasmic component of the embryophore cell, resembles that found in most other taeniids. Three epithelial layers separate the oncosphere from the embryophore. While these layers are narrow and difficult to distinguish, the 'oncospheral membrane' is distinct, darkly stained and relatively thick. The oncospheral hook lies within the oncoblast with its blade portion held by cytoplasmic folds within a modified 'sheath' in the 'basal epithelial layer'. Round, dense bodies are concentrated at the epithelial membranes around the 'sheaths'. Hook muscles insert on the basal lamina at the 'collar' region of the hooks. Penetration gland cells are packed with numerous dense disc-shaped secretory bodies.