ABSTRACT
Ln some species, a single CZ is visualized as a visible pregerminal fold that runs down the length of the testis opposite the epigonal organ. This pregerminal fold appears as a lucent streak and serves as a convenient external marker of the orientation of the spermatogenic wave. As spermatocysts mature they are displaced away from CZ in a coordinated and linear fashion with respect to neighboring spermatocysts, and the maturation sequence traverses the entire diameter of the testis. In Squalus acanthias and other elasmobranchs with this type of testicular ogranization, parallel "columns" of maturing spermatocysts radiate outward from CZ. All spermatocysts, at a given distance from the germinal zone are in the same stage of development, resulting in concentric "rows" of cysts identical in appearance and thus imparting a visible "zonation" in testicular crosssections.
