摘要
It is now well established that in vertebrate striated muscle there are two kinds of filaments, the thick filament and the thin filament. The evidence is strong that myosin is located in the former and actin in the latter. By a direct isolation procedure we could also find tropomyosin in the thin filament. In the smooth molluscan adductor muscle, structural evidence has also been obtained for the presence of two kinds of filaments, but here the thick one is replaced by the very much thicker filament with characteristic 145 A cross-striations. The formal resemblance between the band patterns of this muscle and those of the crystal of para-
