Ultrastructure of the female reproductive system of the lesion nematode, Pratylenchus penetrans (Nemata : Pratylenchidae)

Transmission electron microscopy of the reproductive system of adult female s of Pratylenchus penetrans (Cobb) Filipjev and Schuurmans Stekhoven reveal ed details of oocyte development and the transformation of oocytes into egg s. Oogonial cell divisions were not observed; however, oogonial development into oocytes was distinctive in that most of the nuclei of ovarian cells w ere in the pachytene stage (i.e., prophase I of meiosis). In the midsection of the ovary, the oocytes increase in number, enlarge, and accumulate in a single row. Next, the oocytes enter a muscular oviduct and begin to accumu late lipid bodies and protein granules. The plasma membrane of the oviduct becomes plicated and forms cisternae; centralized membrane junctions establ ish openings for oocytes to enter the spermatheca. Spermatozoa traverse the lumen of the uterus and accumulate in the spermatheca. Each oocyte then pa sses through the spermatheca proximally and then traverses between columnar cells. The posteriad regions of the columnar cells attach to other uterine cells to form the central lumen of the uterus that extends beyond the vagi nal opening and into the postvulvar uterine branch of the reproductive syst em. The fertilized egg is deposited to the exterior after passing between c uticle-lined vaginal and vulval walls supported by anteriad and posteriad m uscle bands, which have ventrosublateral insertions on the body wall.