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Zoology Publications from Victoria University of Wellington—Nos. 68, 69 and 70
Gonad
Gonad.
The gonad consists of a small number of lobes, each lobe comprising numerous acini. Connective tissue septa, containing blood vessels, separate the acini and merge into efferent ductules lined with low cuboidal ciliated epithelium at the bases of the acini. In mature gonads, the walls of the acini are lined with clusters of germinal epithelial cells, and the acini contain both ova and sperm. The ova are always situated peripherally. Each ovum adheres to the wall of the acinus with its free side directed towards the lumen and covered with thin layers of cells apparently derived from the germinal epithelium. As the ovum grows, a cavity appears between this follicular membrane and the developing egg (Fig. 2).
Like the eggs, the sperm arise from cells of the germinal epithelium of the acini. Each male germinative cell develops into a cluster of spermatogonia in which all members undergo a synchronous development (Fig. 3). The cluster apparently becomes attached to a group of germinal epithelial cells, and is arranged with the sperm heads directed towards the periphery of the acinus, and the sperm tails trailing into the lumen (Fig. 4).
In immature specimens, no ova can be seen, although numerous developing sperm may be present (Fig. 5).
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Fig. 2: Cross section of an oocyte fairly late in development, showing the cavity which develops between the oocyte and the follicular cells. Masson's trichrome stain.
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Fig. 3: Synchronous divisions in a cluster of spermatogonia. Haematoxylin/eosin.
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Fig. 4: Cross section of gonad. Sperm are arranged in clumps with heads close to the acinar wall, and tails trailing into the lumen of the acinus. Haematoxylin/eosin.
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Fig. 5: Section through immature gonad, with developing spermatozoa (arrowed). No nurse cells are present. PAS stain.