The Fine Structure and Histochemistry of the Infective Eggs of Dipylidium caninum

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Abstract
The ultrastructure and histochemical composition of the infective eggs of Dipylidium caninum were studied. The uterine capsule is a cellular modification of the uterine lining. Quantities of acid mucopolysaccharide-positive vitelline material within the uterus and uterine capsule form a layer at the surface of the outer capsule of the egg. This material cements the outer capsules together to form clusters of eggs. In the outer capsule a thin lamina separates the outer material from an inner homogeneous PAS-positive layer. Histochemically, a structural polysaccharide or glycoprotein composition is indicated in the outer capsule. The cytoplasmic layer, beneath the outer capsule, contains cell fragments, lipid droplets, mitochondria, and alpha-glycogen. The enbryophore, which surrounds the hexacanth embryo, is composed of 2 layer of rods at right angles to each other. The rods elicit a positive reaction for keratin. The oncosphere contains germinative and somatic cells, 6 keratinaceous hooks with associated embryonic musculature, and a penetration gland. The latter, in the mature oncosphere, has a granular cytoplasm containing small dense elongate bodies. In the infective oncosphere, the cytoplasm of the penetration gland is modified and the dense bodies become swollen and lose their internal structure.