What disc is being referred to in Holling’s disc equation?

Question

The question says it all. I’ve google-searched, but can find any explanation offered for why Holling’s disc equation is called a ‘disc’ equation. https://en.wikipedia.org/wiki/Functional_response

Answer 1

Quoting from http://www.tiem.utk.edu/~gross/bioed/bealsmodules/holling.html:

“Holling's disk equation, named after experiments he performed in which a blindfolded assistant picked up sandpaper disks from a table, describes the type II functional response.”

Holling's original article about this from 1959 is officially here, behind a paywall, but Google also found another pdf.