Note
The fine structure of spermatogenesis is described for the marine calanoid copepod Labidocera aestiva. The mature spermatozoon is a slightly flattened, disc-shaped cell without a flagellum or an acrosome. Primary spermatocytes in first meiotic prophase are characterized by large nuclei showing progressive condensation of chromatin. The cytoplasm contains free ribosomes, numerous mitochondria, cytoplasmic vesicles, centrioles, and perinuclear nuage. Densely staining cisternae are associated with the nuage of pachytene and diplotene primary spermatocytes. This association may represent the temporary differentiation of an acrosome.