[stephen f. polyak]

Nice photo Roger! :-)

Short vertical object ("aerial") beneath the wing is in fact a graduated tube (glass) with slotted metal protective sleeve to provide visual indication of wing-tank fuel quantity to the pilot.

I suspect that the tank-like object beneath the fuselage is, just that, a (fuel) tank or maybe a container. It is unnecessarily big for a camera, and to put a transparent nose immediately aft and below the oil cooler as well as engine is asking for frequent staining; that makes for terrible photos. Moreover, if a camera, the pointing direction would favor downward, not ahead or upward. Why make the entire dome transparent? Could the dome, perhaps removable, be of a different material or painted a different color, or just oil-stained? Thus, the image we see.

Most interesting to me are the two rectangular outward-rearward extensions beneath the cowing. On a typical Fi 156, that is where the engine exhaust discharges. Perhaps these keep the exhaust heat/smoke/flame off the tank.