We looked aloft.

Directly above the troops, flying as straight for Brussels as a homing bee for the hive, went a military monoplane, serving as courier and spy for the crawling columns below it.

Directly, having gone far ahead, it came speeding back, along a lower air lane and performed a series of circling and darting gyrations, which doubtlessly had a signal-code meaning for the troops.

Twice or three times it swung directly above our heads, and at the height at which it now evoluted we could plainly distinguish the downward curve of its wing-planes and the peculiar droop of the rudder -- both things that marked it for an army model.

We could also make out the black cross painted on its belly as a further distinguishing mark.
To me a monoplane always suggests a bird when it does not suggest an insect or a winged reptile; and this monoplane particularly suggested the bird type.