Ultrastructure of Pharyngostomoides procyonis Harkema 1942 (Diplostomatidae). I. Observations on the male reproductive system.

Spermatogonia, nutritive cells, and developmental stages of spermatids were observed with the electron microscope. Spermatogonia are near the surface of the testis and contain large nuclei and comparatively little cytoplasm. Nutritive or supporting cells are associated with the spermatogonia. Early spermatids are characterized by a circle of mitochondria around the nucleus. Late spermatids have 2 parallel free flagella separated by a cytoplasmic process, and a nucleus containing electron-dense strands of chromatin arranged in coils or concentric layers. Mature sperm have 2 flagella enclosed by cytoplasm. Their nuclei contain dense, fibrillar chromatin. A microtubule-organizing center (MTOC) found between basal bodies of spermatids is described. Descriptions are presented of the seminal reservoir, seminal vesicle, and the sperm found in those organs.