Scanning electron microscopy and histochemistry of embryonic envelopes of the porcupine tapeworm, Monoecocestus americanus (Cyclophyllidea: Anoplocephalidae)

Abstract

Eggs of Monoecocestus americanus (Stiles 1895), a tapeworm of North American porcupines, were studied with regard to the basic structure of embryonic envelopes. Observations were made by light microscopy of whole eggs and scanning electron microscopy of eggs within cryofractured gravid proglottids. Concomitant histochemical tests were made on eggs and gravid proglottids embedded and sectioned in methacrylate plastic. The gravid uterus had numerous diverticula, each containing several eggs. The uterine lumen was filled with a material positive for nonsulfated acid mucopolysaccharides. The material adhered to the eggs, giving them their characteristic spinose surface when teased from the proglottid. Each egg included an oncosphere larva surrounded by an oncospheral membrane, pyriform embryophore, inner and outer envelopes, subshell membrane, and embryonic capsule. Overall, the structural and histochemical characteristics of these layers were similar to those described for other cyclophyllideans, with only minor variations.