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Ultrastructure of the Sperm Duct and Penis Bulb of Dugesia tigrina (Platyhelminthes: Tricladida)
Transactions of the American Microscopical Society
Vol. 109, No. 2 (Apr., 1990), pp. 141-151
Stable URL: http://www.jstor.org/stable/3226808
Page Count: 11
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Dugesia tigrina displays two sperm ducts. Each consists of three morphologically different segments. Their basic histological structure is that of an epithelium bounded by a basal lamina and a noncontinuous circumscribing musculature. The anterior segment has a permanent lumen and no surrounding muscle fibers. The middle segment, also lacking muscle fibers, is the spermiducal vesicle. The duct wall of this segment becomes thinner and finally ruptures when overfilled, allowing individual spermatozoa to escape into the surrounding parenchyma. Layers of muscle fibers increase in the posterior segment as the duct approaches the penis bulb. I postulate that peristaltic movement of the duct wall may be responsible for the portioned release of spermatozoa into the penis bulb. All secretory material found in the assembled sperm mass is contributed by two types of glands located in the penis bulb wall, their gland duct portions opening into the bulbar lumen. Following copulation, the penis bulb lumen collapses and only a slit-like space remains until the secretory cycle is reinitiated. Although no sphincter muscle occurs at the entrance to the ejaculatory canal, no spermatozoa or secretory material is released into the canal prior to copulation.
Transactions of the American Microscopical Society © 1990 American Microscopical Society