This is an Alaska whitefish, a cousin of the salmon whose genus name, Coregonus, means “angle-eyed.”
But this isn’t the eye. It’s the alimentary canal, the guts, taken from a dissection done for the 1904 edition of Proceedings of the American Philosophical Society held at Philadelphia for promoting useful knowledge. It’s useful to know how to gut a whitefish, for sure. But this fish traveled before the image was made — it’s an Alaskan fish but was studied by Henry Fowler in Philadelphia as a way of helping describe what made this Alaskan whitefish an Alaskan whitefish: “As this species is only known from Dr. Bean’s description and several references, it is of value to have more detailed information for the comparison of the species.”
It has a large spleen, as you can see.