You cite something called APE format. After teaching 9th grade English for several years, I can honestly say I do not know what that is. You may be asking about APA format, a notation method.
Either way, on enotes.com, our service is to provide an answer to your question generally in paragraph form.
Whitney seems to serve as a foil to Rainsford. A foil is a character often close to the protagonist who helps highlight the main character's traits by being different and almost exactly opposite of the main character. In this story, Whitney is different from Rainsford in a few ways. First, he believes the superstitions that the seamen have are well-founded. Whitney feels and experiences the fear that is in the air. A second distinction between the two further develops the contrast between fear and bravery. This occurs as Whitney discusses the fear of being killed that a jaguar might have. Rainsford disagrees and blows off the idea entirely because jaguars are just animals. These differences help develop the character traits in Rainsford of bravery and confidence. We also see him as a hunter in the opening scene and these traits fit him well. We would not get such a great picture of Rainsford without Whitney.