The above graphic demonstrates the fine touch pressure thresholds of the human penis in its intact and circumcised states. Note that the most sensitive parts of the penis are contained within the prepuce (foreskin) and that the amputation of the prepuce leaves very few of these sensitive areas behind. The prepuce is an organ present on the clitoris and penis of all mammals at birth, and serves many functions, including that of sexual pleasure and sensation.
Source: Sorrells ML, Snyder JL, Reiss MD, et al. Fine-touch pressure thresholds in the adult penis. BJU Int 2007;99:864-9. Full study available for review at: http://www.cirp.org/library/anatomy/sorrells_2007/