ἐν αὔ, ιις τρέφεται=“ἐξ ἀνέμων τρέφεται” (schol.). With “τρέφεσθαι”, the prep. ἐν usu. denotes the surroundings of the “τροφή”, as Plat. Theaet.p. 175 D “ἐν ἐλευθερίᾳ...τεθραμμένου”: but it can also denote, as here, the aliment; id. Plat. Tim.p. 81 C “τεθραμμένης...ἐν γάλακτι”.