The Genital System of Temnocephala. I. Ultrastructural Features of the Differentiating Spermatid of Temnocephala Novaezealandiae, Including Notes on a Possible Correlation Between Cellular Autophagy and Mitochondrial Function.

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Abstract
The early spermatid of I: novaezealandiae possesses two centrioles, between which lies a transient lamellar body. The centrioles form the basal bodies of two flagella of the '9+1' type, which remain free throughout spermatogenesis. Following cell elongation and organelle migration, the advanced spermatid is composed of a proximal cytoplasmic mass, a greatly attenuated nuclear region, an elongated mid-piece, an end piece, and the subterminally inserted flagella. There is no acrosome. Rows of glycogen granules occur in the spermatid shaft. Extrusion of nuclear components probably contributes to the modelling and compaction of the nucleus. The mitochondria of the cytoplasmic mass possess indentations filled with membrane whorls; it is proposed that the membrane accumulates in cellular autophagy. Mitochondria in the spermatid shaft are also indented; perhaps autophagic vesicles occupying the invaginations are related to glycogen metabolism. Modified membranes lining the indentations may be sites for the entry of lytic products into the mitochondria. Knowledge of the sperm morphology of Temnocephala assists in the determination of the taxonomic position of the genus.