2,5/5. I got to say that I'm closing this book with a bit of a disappointment. The first third of it was interesting, but then it get a bit repetitive, the organization become a problem, because the author seem to lost herself a bit into digression and the focus point of the book was lost, or at least it felt that way to me. We get a bit of evolutionary theory, a lot of stuff about the shell, a lot of anatomy too, etc. The information was great and if you're new to the subject you will learn stuff. Unfortunately I'm not totally new to the subject, I already read some book on it, and I didn't learn as much as I would have like and the organization and the structure of the book seem problematic to me.