Internal Citation

If the resource in question has page numbers, cite per usual.

But if not, the APA Guide to Electronic Style says,

"For electronic sources that do not provide page numbers, use the paragraph number, if available, preceded by the ¶ symbol or the abbreviation para. If neither paragraph nor page numbers are visible, cite the heading and the number of the paragraph following it to direct the reader to the location of the material."

So where paragraph is numbered: (Thompson, 2002, ¶ 4)

Where it is not: (Thompson, 2002, Internal Citation section, ¶ 4)