The fine structure of the ovary of the feather star Nemaster rubiginosa (Echinodermata: Crinoidea).

The outer layer of the crinoid ovary consists of coelomic epithelium, smooth muscles, and nerve cell processes. The middle layer of the ovary contains non-germinal accessory cells, small germinal cells (either oogonia or pre-leptotene primary oocytes), and post-pachytene primary oocytes; all these cells are completely embedded in a haemal matrix of 200 A-diameter granules. The primary oocytes larger than 20mu in diameter have abundant invaginations in the plasma membrane, suggesting uptake of materials from the haemal matrix. The innermost layer of the ovary is a ciliated epithelium lining the cell-free ovarian lumen.