The distribution of the zebra mussel byssus gland cells in mussel foot. The zebra mussel foot sections are stained by H&E method. The sections are made along the longitude axis as demonstrated by the paralleled dash lines across the foot. Arrows with dashed line indicate the position of the three major byssal glands embeded in the mussel's foot. a: A longitudinal section in the root of the mussel's foot. Arrows point to the stem-forming glandular cells (S). b: The section of middle area of the foot. The light purple cells along the epethelial surface of the foot were thread-forming cells which were demostrated by arrows and the letter T. c: The tip of the foot containing the deep purple stained plaque-forming gland cells that were labled as P.