Electron microscope and histochemical studies on the oncosphere of Hymenolepis nana.

The ultra and histochemical structures of the oncosphere of Hymenolepis nana were studied. The oncosphere is surrounded by several protective layers. The outer envelope appears to be cellular in origin and consist of an electron dense outer zone and an inner granular zone, mucoprotein in nature. The inner envelope and embryophore are a continuous morphological unit of a protein structure. Within the oncosphere, apart from hooks, there are two germ cells, two somatic cells and a large penetration gland. The oncospheral hooks consist of three layers and elicit a positive reaction for keratin. The penetration glands fill the posterior region of the embryo and contain granules of varying density and shape.