Fig. 2. Preparation used to measure isometric twitch forces from mechanically isolated dl₁ muscles. (A) Placement of the anterior (a) and posterior (p) muscle grips for twitch force measurements on mechanically isolated muscles. (B) After decapitating the moth, the 1st phragma was exposed and the anterior grip placed over the anterior insertion of the dl₁ muscles. The paired needles of the posterior grip were driven through the dorsal cuticle and down along the posterior face of the 2nd phragma. Both grips were secured to the exoskeleton with cyanoacrylate adhesive. After gluing acetate strips (not shown) across the gap between the two grips to fix their relative positions, cuticle strips were excised (arrows, broken line) to mechanically isolate the anterior grip and muscle insertions from the rest of the thorax. The anterior grip was then secured to the force transducer via the threaded rod projecting from the grip. The ball bearing (bb) mounted on the posterior grip fit into a depression in the end of a threaded rod (tr) mounted on a translation stage. When secured by a slotted retaining nut (n), the ball bearing and threaded rod formed a ball joint. The acetate strips spanning the two grips were then cut, and any misalignment of the cut ends was corrected using the ball joint and translation stage.