Hi Arenzano, I don't know what level of detail you're looking for, but what you can do is look up articles about histolysis (that's the digestive-like process where the pupa breaks down parts of the old larva body for re-use), histoblasts (also called the imaginal buds or discs, which are groups of cells that are present but hidden and non-functioning in the larva, but which don't get digested -- they are responsible for forming specific structures and organs in the adult butterfly) and/or histogenesis (the general name for the process of building tissues and organs from undifferentiated cells). They'll have the information you want.
I have seen some older research projects where scientists did identify specific histoblasts from the larvae of other species, but I don't know of one specifically for monarchs. They were investigating what would happen if, for instance, they carefully removed the hindwing histoblasts from the larvae, then allowed them to complete their development. What they got was a butterfly with larger forewings, suggesting that since the amount of soup in the pupa is limited, if some histoblasts aren't present to use up some of it to make their structures, then some of the others might be able to get more.
If you want to dig really down deep in the biochemical details, try looking for the set of books called Comprehensive Molecular Insect Science. Way beyond my budget, LOL.
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