Sentence:  Then immediately were my shape and my mental-faculties distored, and horn-furnished, as ye see, I with frantic speed, by the sharp-mouthed gadfly stung, rushed to the thirst-assuaging stream of Cenchréa, and the fountain of Lérna—whilst the Earth-born herdsman Argos, zealous in anger, followed me, <WSD>lookful</WSD> on my steps with many eyes. 
Meaning of the word marked with <WSD> tags:  Looking carefully; observant.