Reddit reviews The Annotated Origin: A Facsimile of the First Edition of On the Origin of Species

If you are determined to read it, I suggest reading the original and not any of the "abridged" editions. Also, the first edition should be your go-to, as latter editions have a lot of rebuttals to various criticism of the work.

Having read it myself, I can recommend that you read this annotated version "The Annotated Origin: A Facsimile of the First Edition of On the Origin of Species" (https://www.amazon.com/Annotated-Origin-Facsimile-First-Species/dp/0674032810)

I highly recommend Darwin's "The Origin of Species [by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life]." It sets the groundwork for a lot of modern biology, while also being an outstanding philosophical endeavor (his second work, "The Descent of Man" even moreso, but it also carries some cultural artifacts that are less than ideal these days). Despite what you might assume, it does not require much technical understanding, and is not nearly as dry as modern scientific papers. I honestly very much enjoyed reading it, and Darwin does an amazing job of explaining himself. I highly recommend an annotated version of Origin with the illustrations from his notebooks.

EDIT: I recommend either this illustrated version or this annotated version. These have the first edition text, crisp and clear and strong, and not nearly as watered down as some of the later editions of Origin. I've heard that this particular annotated version is considered one of the best ever produced, so it's probably your best bet.

You can always check out textbooks, my vertebrate zoology textbook was fun

Veterinary textbooks are a good way to learn about anatomy

If you haven't already done so Darwin's Origin is a must read. While not directly zoology, its helpful in understanding the theory of evolution, a cornerstone of biology and a HUGE component of zoology (90% of my zoology class was evolution based). The prose can be dense so I'd recommend an annotated version (my old professor wrote a good one https://www.amazon.com/Annotated-Origin-Facsimile-First-Species/dp/0674032810)

As a heads up, zoology is an incredibly vast field, that's like saying I'm a doctor, what kind of doctor? GP? Cardiologist? ENT? You know what field you want which is great! But you may want to look into what you want to do from the field.

Best of luck!

See if you can lay hands on the one annotated by James Costa (or someone else, his is just the only one I'm aware of). My copy is just to the left of me. It's fantastic.

Comes in hard and soft flavors.