This was said of persons who were seized with a sudden commotion or disturbance ot the mind, as poets by the inspiration of the Muses, from some resemblance in their conduct, as it was supposed, to cattle that had been bitten by the œstrum or gad-fly. It is known that cattle have such extreme horror of this insect, that on only hearing the noise it makes when flying, they run about the fields as if they were mad. The adage was also used when any one was seen to apply himself intensely to any kind of business, or study. « But what fly,» Friar John says, « has struck Panurge, that he is of late become so hard a student?» What maggot, we say, has he got in his head.