Fig. 3. Structural organization of the male reproductive system in the mantle of 1-year-old (A—D) and adult (E,F) mussels. (A) Dorsal view of the right (R) and left (L) shells; a—p, anterior-posterior axis; v—d, ventral-dorsal axis. (B) Paired tubular gonad and reproductive tract spreading into a two-lobe mantle sheet (whole-mount histology). (C) View of the tubular gonad network in one mantle lobe (whole-mount histology). (D) Detailed view of the ejaculatory bulb-like structure (whole-mount histology). ST, spermatogenic tubule; TGD, transversal gonad duct; LGD, longitudinal gonad duct; EB, `ejaculatory' bulb-like structure. (E) The ST-network occupies almost the entire volume of the mantle lobe in adults. (F) Sperm emission (SP) through the EB-like structure. G, gills; PAM, posterior adductor muscle. Scale bars, 1 mm (A); 0.5 mm (B,E); 0.2 mm (C); 0.1 mm (D); 2 mm (F).