The best source I can think of is Polis' Biology of Scorpions . . . you may be able to find the relevant pages on Google Books.
I have a "kid" book called A Look Inside Spiders and Scorpions: a Unique First Visual Reference that has some internal diagrams on transparent pages so you can see them individually or layered.
Link: http://www.amazon.com/Spiders-Scorpions-P-D-Hillyard/dp/0895778009
You might find it in a bookstore where you can flip through it in person.
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