On the concepts of Species, Variety, Race, and Breed in Origin of the Species.?

I am about a fourth of the way through this book, and it is clear that these terms were not used then in the same way they are now. For one, we have a clear definition of species. If a pairing produces fertile offspring, they are in the same species. These terms in this book however seem to greatly overlap. Can someone help me understand their distinctions?
 
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