A priori = a posteriori?

"Most certainly Hume was wrong when he wanted to derive all that is a priori from that which the senses supply to experience. Adaptation of the a priori to the real world has no more originated from 'experience' than has adaptation of the fin of the fish to the properties of water. Just as the form of the fin is given a priori, prior to any individual coping of the young fish with the water, and just as it is this form that makes possible this coping: so is it also the case with our forms of perception and categories in their relationships to our coping with the real external world by means of experience." (Lorenz 1962, Kant's Doctrine of the a priori in the Light of Contemporary Biology, p. 25)