Yes, although it hasn’t been until recently, with certain advancements in technology, that we could do it. Forretress shells are exactly as hard as you’d imagine, after all.
(Don’t worry, readers. The forretress used for scientific purposes are typically donated to science upon death. Most scientists wouldn’t cut into live forretress.)
In any case, the interior of a forretress is pretty well-documented, but you may wish to consult the texts by Professor Oak on the basics of bug-type physiology if you’re looking for specifics.
The Pokédex According to Bill 