Ovulation in the sea cucumber Stichopus

Full-grown oocytes of the sea cucumber Stichopus are encased in follicles and arrested in prophase of meiosis I with a large, clear germinal vesicle and nucleolus. Near the site at which the follicle attaches to the ovarian tubule wall the oocyte extends a "protuberance" (clearly visible in the top left image below). During ovulation the oocyte oozes, protuberance first, out of the follicle, taking with it a lacy jelly layer. The top rightmost image show an oocyte just beginning to de-folliculate, and the bottom row shows various intermediate stages... usually the oocyte takes a few minutes to ooze out, but some of them get stuck!

These eggs were obtained from dissected ovaries. Ripe ovarian tubules can be teased open with forceps, and follicles usually fall away from the tissue fairly readily. Unfortunately I have never seen this procedure result in more than about ten percent of the eggs successfully completing maturation and fertilization.