DC motor field question

Hello:

I'm replacing a Variac speed control (adjustable DC supply) for a 1/3 hp dc
motor with an electronic drive. I'm puzzled by the motor wiring.

The motor says compound wound elec. rev. which I take to mean electrical
revese or electrically reversible. Because that is normally possible anyway
simply to reversing the armature, it suggests there is something in the
motor's wiring that is uniquely characterized for electrical reverse.
Armature is 115 VDC 3.4 A and field is 115 VDC 0.4 A.

With this assumption, I am attempting to interpret a weird field wiring
described below.

2 leads measure 3-10 ohms, rotor position dependent. This suggests brush
resistance and low resistance suggests the winding that handles current.

There are 3 more leads that measure 300 ohms between each pair, and
essentially a short (1 ohm) across the whole thing...looks like two windings
in series, or centertapped, then 'folded over' to connect the upper and
lower ends...what I am describing could also suggest that they are
paralleled. I doubt a short - that is more likely to happen on the armature,
and the two windings are identical - how likely is it a short could develop
that allows symmetry? Not very in my opinion.

The old wiring diagram doesn't show any of this weirdness, so perhaps the
motor has cababilities that were never used, like maybe a dual voltage
field. I also wonder if there is an analogy with transformers wherein
windings can be paralleled (like dual primary) without changing the turns
ratio or flux, but series does affect the turns ratio...contradicting any
intuitive analogy between series and parallel inductors (separate ones not
sharing the same core, which links the flux).

Anyone have any insight or answers? I'm not sure guesses will be
helpful..I'm doing enough of that already.

Thanks

Murray