POSTEMBRYONIC DEVELOPMENT OF THE OVARY IN THE PENICILLATE DIPLOPOD, EUDIGRAPHIS NIGRICANS (MIYOSI) (DIPLOPODA, PENICILLATA)

Postembryonic development of the ovary through the larval stages was s tudied in a penicillate diplopod, Eudigraphis nigricans. In the first instar larva a single young cell cluster, consisting of about 20 spher ical genial cells and some smaller interstitial cells, exists beneath the alimentary canal in the third body segment. The gonadal epithelium encompasses the upper surface of this young cell cluster by the end o f the first instar. The epithelium then extends forward and backward t o form a single long sac-like gonad, leaving the young cell cluster on the center of the gonadal floor as a mound-shaped germarium. In an ea rly second-instar larva, very early previtellogenic oocytes accompanie d by some interstitial cells appear in the front and rear surfaces of the ovarian germarium. During the period from the third through the se venth (the last) larval instar, some cell clusters containing several previtellogenic oocytes and interstitial cells successively separate f orward and backward from the germarium to form a series of paired patc h-shaped vitellarial areas on the extending ventral ovarian epithelium . In each vitellarial area, some of the interstitial cells surround th e oocytes to form the follicles. In the seventh instar, the ovarian lu men is extremely expanded, and the late previtellogenic oocytes in the vitellarial areas encroach upward into the ovarian lumen. These oocyt es floating in the ovarian lumen are still connected with their own vi tellarial areas by partial extensions of their follicles. Some phyloge netic implications of the basic characteristics in structure and poste mbryonic development of the ovary are discussed. (C) 1995 Wiley-Liss, Inc.