Full Idea
Flesh is not the ultimate sense-organ. To suppose that it is requires the supposition that on contact with the object the sense-organ itself discerns what is doing the discerning.
Gist of Idea
Sense organs aren't the end of sensation, or they would know what does the sensing
Source
Aristotle (De Anima [c.329 BCE], 426b16)
Book Reference
Aristotle: 'De Anima (On the Soul)', ed/tr. Lawson-Tancred,H.C. [Penguin 1986], p.194