To get this photo, I first split the hollow, narrowly cylindrical culm along its length. Then I took one of the resulting split pieces and cut its end perpendicular to its length, as carefully and neatly as I could, creating, in effect, a cross-section of the split piece. So this photograph is an end-on (or cross-section) view of that split piece. The same split piece of culm is shown (from other angles) in the earlier images in this series.

What you see here, in cross-section, are two adjacent tunnels made by a Thrypticus larva in the interior culm tissue.

Ruler units are sixteenths of an inch