Two types of very long visual fibers found in the optic lobe of the flesh-fly, Boettcherisca peregrina.

Horseradish peroxidase (HRP) uptake (through a Corneal incision) in photoreceptor cells of the compound eye of Boettcherisca peregrina, resulted in the labeling of two types of very long visual fibers. One of them (the long fiber, If) penetrates through the lamina and medulla, and directly terminates within the lobula. The other (the bypass fiber, bpf) terminates in the medulla, like the axons of R7 and R8 photoreceptor cells, but the fibers run a considerably roundabout course. The photoreceptor cells with these very long fibers are region-dependent within the retina. Both the If and bpf are found almost exclusively in the male fly.