Abstract: The histology of the gills of M.asperulum was studied with section technology. The result shows that M.asperulum has seven pairs of phyllobranchs, and every one of them consists of a gill axis and many gill lamellae. The gill axis is composed of connective tissue, and has a vas afferens in its dorsal side and a vas efferens in its ventral side. The gill axis also contains a lot of gill glands,nephrocytes and nurse cells. The lamella is a basic respiratory unit of gill, and its wall is composed of a single l...