I've actually always wondered that myself koshmar and i can't honestly say I have a good answer for that. It may be that it requires a lot of energy to have them, so if they aren't being put to use, they might as well not have them and reallocate that energy into growth or reproduction. but then why regenerate them afterwards? It might also be that since the rapts are basically one big muscle, that such amounts of stored energy might actually break down the limb from the inside for some biochemical reason (apoptosis maybe?)... who knows? Dr. Roy might, hopefully he chimes in.