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hello Jorge,

Chitin, as a major component of the arthropode integument, is 'per se' not so hard or 'sclerotized'. Sclerotization happens by addition of some protein (arthropodin), that gets hard when phenolated ('tanning' ), or some carbonate (e.g. in lobsters and such). At articulations etc. where the exoskeleton must be flexible, chitin is also present, but thinner and softer (not or barely sclerotized).

So the wings of insects are not principally different from the rest of the exoskeleton, they are mostly chitin and protein. The veins are derivates of tracheae (breathing tubes), that are necessary for stability and for the inflation (spreading) of the wings after moulting (the wings are literally pumped up).

Hope that befuddles ;-)

martin (heavily experiencing his limits of writing in a foreign tounge).

p.s. Halteres, in some way, ARE wings ... no special chemistry here.