Mode of Reproduction and Development of the Reproductive System of Helicotylenchus Dihystera

Abstract

The morphology of the adult female reproductive system was studied in Helicolylenchus dibystera and H. digonicus. In both species, it was found to comprise the following parts: Ovary (8.7 to 21.2 oogonia and oocytes in anterior gonad, 7.6 to 18.3 in posterior gonad of H. dihystera), narrow .constriction (four cells), tubular oviduct (sixteen cells), constriction (eight cells), dorsally bulging, nonfunctional spermatotheca (twelve cells), glandular tricolumella (twelve cells) and uterus proper. The final number of cells making up the spermatotheca is determined during the last molt, no cell divisions take place later in the adult. No spermatozoa could be demonstrated in the spermatotheca or in any other part of the gonoducts and reproduction was by mitotic parthenogenesis. The cells of the tricolumella have a secretory function and the material they produce appears to be deposited on the surface of the eggs. The post-embryonic development of H. dihystera comprises four larval stages and the adult. The first molt takes place within the egg. The three larval stages outside the egg can be recognized on the basis of the degree of development of the reproductive system. The reproductive system of each larval stage has a constant number of nuclei. Nuclear divisions in the reproductive system occur only during molting, whereas cell enlargement takes place mainly during the larval stages. The reproductive system consists of four nuclei in the second larval stage, fourteen nuclei in the third and 108 nuclei in the fourth larval stage. The final differentiation of the various gonadal parts takes place during the fourth molt. Specialized ventral chord nuclei and some other nuclei outside the gonad whose origin could not be determined take part in the formation of the vagina. One of the central nuclei of the gonad proper appears to function as vaginal organizer (I nucleus).