MORPHOLOGY AND FINE-STRUCTURE OF THE GRAVID UTERUS OF 3 HYMENOLEPIDIDTAPEWORM SPECIES (PLATYHELMINTHES, CESTODA)

The ultrastructure of the uterus in gravid proglottids of Hymenolepis citelli, Vampirolepis nana and Vampirolepis microstoma was examined us ing transmission and scanning electron microscopy. The cellular and su bcellular structures were similar in all three species, consisting bas ically of a syncytial layer attached to a basal extracellular matrix. All nuclei were juxtaluminal and each contained a single large central ly located nucleolus and prominent masses of central and peripheral he terochromatin. The cytoplasm showed evidence suggesting a high level o f protein synthesis and secretion. It consisted primarily of granular endoplasmic reticulum with moderately dilated cisternae; most cisterna e were completely filled with an electron-lucent flocculent material, but others contained electron-dense granules. Free ribosomes and mitoc hondria were also present. The apical plasma membrane and a small amou nt of enclosed cytoplasm were folded into long microlamellae that exte nded into the uterine lumen. Larger epithelial folds and villi consist ing of folded portions of the entire epithelium projected into the ute rine lumen. The uterine epithelium along with its basal extracellular matrix and underlying cellular parenchyma were folded into the lumen a t several points, forming epitheliomesenchymal folds and villi that cl osely apposed many of the eggs.