Definition of "protrudable"

The males, and rarely the females, of many kinds of bats have glands and protrudable sacks situated in various parts; and it is believed that these are odoriferous.

1874, Charles Darwin, “Secondary Sexual Characters of Mammals—continued”, in The Descent of Man, and Selection in Relation to Sex. […], 2nd edition, London: John Murray, […], Part II (Sexual Selection), page 529