Spermatogenesis in a nematode Nippostrongylus brasiliensis

The structure and development of the spermatozoon of Nippostrongylus brasiliensis was studied with the electron microscope using thinsectioned material and tissue prepared by the freeze-fracture technique.The developing germ cells are connected via a complex anucleate rachis which begins as fine threads of cytoplasm joining the spermatogonia. It rapidly enlarges to a broad, central core which not only anchors and joins the spermatocytes, but also appears to be an important site for protein synthesis. Formation of membranous organelies (MOs) from RER-associated Golgi bodies dominates the activities of the growing spermatocytes. As the latter approach meiosis, the rachis declines in importance and finally becomes the site of breakdown of the residual cytoplasm. The spermatid chromatin condenses into a long cylinder during spermatogensis. A pair of centrioles in an indentation at the anterior end are believed to organize long microtubules which are responsible for moving the nucleus through then out of the sperm cytoplasm to form a tail-like structure. Thus the cytoplasmic region of mature sperm contains only mitochondria and MOs; a small part of the anterior is amoeboid.