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Acta Parasitologica, Vol.44, No. 1, 1999, 4-10
Conn David Bruce - Ultrastructure of the embryonic envelopes and associated maternal structures of Distoichometra bufonis (Platyhelminthes, Cestoidea, Nematotaeniidae).

School of Mathematical and Natural Sciences, Berry College, Mount Berry, Georgia 30149-5036, U.S.A.

Eggs within paruterine capsules of gravid proglottids of Distoichometra bufonis were examined by light and transmission electron microscopy. The embryonic capsule was membranous, but was immediately underlain by a non-uniform subcapsular lamina that was an intracellular component of the outer embryonic envelope. The subcapsular lamina was thick and semi-rigid on anterior and posterior poles, but thin and membranous laterally, giving the entire egg a laterally oblong shape. In contrast, the embryophore was spherical and uniform in thickness. The paruterine capsule walls were derived from layers of flattened processes of medullary parenchyma cells lined internally with a layer of uterine epithelium. All these layers extended inward to form parenchyma-uterine partitions segregating each egg into an individual chamber. The uterine epithelium was very thin, syncytial, and contained numerous vesicles. Little uterine secretory product occurred in the uterine lumen or on the outer surface of the embryonic capsule. Except for the unique subcapsular lamina, most features of the eggs and paruterine capsule resembled those of other nematotaeniid species. The paruterine capsule wall was similar to that of Mesocestoides lineatus, a species whose paruterine organ lacks parenchyma-uterine partitions.

KEY WORDS: cestodes, nematotaeniids, Distoichometra bufonis, ultrastructure, embryonic envelopes
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