Re: What are those hairs in a fruit flies eye?

In general, Drosophila bristles are either chemosensory or mechanosensory;
those on the eyes are mechanosensors, and send signals directly to the
brain.  Although these sensory hairs are often labeled as being parts of
the ommatidia, each ommatidium's hair comes from a developmental lineage
separate from that of the other portions of the ommatidium, so your
description of the hairs as being "between" the ommatidia might actually be
more accurate.

References:
 http://www.sdbonline.org/fly/vdevlhom/movie.htm