Footkerchief:
Then organs should be divided into cumulative (eyes for seeing, legs for walking, kidneys for...) and necessary (vocal cords and tongue for speech).
I agree. It's just that it can't be done with the current organ format since, like I was saying, the game doesn't know that a left kidney and right kidney are both kidneys and are therefore
cumulative with regard to each other -- they just have the word "kidney" in common, and that's not enough.
It would have to be like [REDUNDANCY:ORGAN_KIDNEY], a tag applied to ALL of the kidneys so that the game could use the string "ORGAN_KIDNEY" to know that the kidneys are redundant with each other. What string you use doesn't matter as long as it's unique within the body, it's just a declaration of a "redundancy class." So for the octopus, you would have the main heart with no redundancy tag, plus the two gill hearts which would have a tag like [REDUNDANCY:HEART_GILL]. Bingo.
Anyway, I'm just going on about this because I think the DF body tree system is fascinating. Toady probably already implemented a better solution along with all the other organ changes.
I wonder if "send in a chitin tissue to fill the skin role in the exoskeleton plan" means that you actually create the chitin in the creature material list and then send that material. I suppose for things like iron men you would also have to be able to pass materials from outside the creature definition, i.e. iron. This lays the framework for some amazing stuff, like an antman's exoskeleton melting off his body based on the chitin material's melting point, etc.