(The word of the day is taken from the Torre Bueno Glossary of Entomology… this one was chosen by a lab member)

Proctiger, reduced abdominal segment X, bearing the anus.

Just to illustrate the maturity level in this lab.

It may also be referred to as: For ♂: anal cone, anal lobe, anal segment, harpago, harpe, lobe of tenth sternite, tenth abdominal segment, tenth segment, tenth sternites; for ♀: anal cone, anal membrane, anal protuberance, anal segment, peri-anal membrane, segment X, tenth segment; for pupae: anal lobe, anal segment, genital pouch, ninth sternite, tenth abdominal segment, tenth segment, segment X. (source)

And here is where you might find the proctiger of a fly:

The proctiger may also be found in Hemiptera (Psyllidae and Heteroptera) Raphidoptera,, Neuroptera, Trichoptera, Strepsiptera, and Coleoptera. Now you know.