Abstract Liu, L. L. and Wang, S. P. 2002. Histology and biochemical composition of the autotomy mantle of Ficus ficus (Mesogastropoda: Ficidae). — Acta Zoologica (Stockholm) 83: 111–116 When the foot of the figsnail Ficus ficus is mechanically stimulated, a portion of the mantle on the side of the inner lip, recognized as the autotomy tissue, swells then autotomizes. Studies of the behaviour and population dynamics of mantle autotomy in F. ficus have previously been reported, but here, a detailed description of the structure of the autotomy tissue is presented for the first time. Whether or not this autotomy tissue has the secondary function of a storage compartment was also investigated through analysis of its biochemical composition. Figsnails were collected from the coast of Kaohsiung, Taiwan. Histological observations indicated that the most obvious feature of the autotomy tissue is the extensive network of muscle fibres and connective tissues. In the swollen autotomy tissue, not only do the epithelia rupture, but the connective tissue expands threefold on the dorsal side and 15-fold on the ventral side. Chemical analysis of body composition indicated that the average contents of protein, lipid, carbohydrate and ash in the foot, mantle and autotomy tissue are in the range of 55.6–76.5%, 0.6–14.1%, 2.0–27.9% and 6.5–13.5%, respectively, with the caloric value ranging from 4.7 to 5.5 kcal g−1 dry wt. The content of carbohydrate in the autotomy tissue is much less than that in the foot and mantle, i.e. 2.0–6.8% vs. 13.0–27.9%. There is no indication that the autotomy tissue serves as an energy reserve. Hence, it is suggested that the autotomy tissue functions only as a defensive weapon.