This sample holder is a spring-mounted "Bonanni" style. Specimens were mounted usually in an ivory slider, which slid into a spring-loaded slit. There are no lenses in this component.
The curved slot in the stage insert was used to hold a glass vial (containing an "aquatic" specimen)
The brass cone (B) fits in the base of the sample holder (A). It was designed to "intercept some of the rays of light". Thus it acted like a substage aperture to reduce light scattering.
Underneath the stage is this spring clip. It retains the fishplate in place.