Turns out the mystery is solved.

An answer was supplied to myself on another board by a participant
with the handle of Heliopause

The image originated in a German propaganda magazine dating from
January 1941 called Der Adler.

Turns out there was a caption on the page that I didn't think was
associated with the image. (I read and translated every damn thing on
the page EXCEPT for the crucial caption. DOH! Here is the caption and
the rough translation.

Zum bilden unten: Um stromungsgeschwindigkeiten und anströmrichtung am
leitwerk des flugzeugs zu messen, wird ein grosser verspannter mast
mit zahlreicher messdüsen, scherzhaft "weihnachtbaum" genannt,
angebracht. Von den düsen führen rohrleitungen nach dem manometerbrett
vorn in bezatzungsraum.

Roughly this means:

To measure (air)flowspeeds and flowdirection at the tail of the
airplane a big mast is attached with numerous measurement equipment,
nicknamed "Christmas tree". From the openings pipes lead to the
manometerplate in the cockpit.

So unless the caption is an effort at wartime deception - that appears
to be the answer!

I had also though of another possibility, that perhaps it was some
sort of equipment for laying smoke. I have seen such equipment on a
Stuka and on a P-38. But it appears not.

Thank you all for trying with your suggestions.

Waldo.


P.S. About waveguides. I didn't think that they were waveguides, but
did think it possible that they were insulated wiring. The cabling of
the period was quite robust. But I guess not.