Unveiling the butterfly diagram structure

A Butterfly Diagram showing the spotted area distribution is presented. The diagram reveals that most of the spotted area is concentrated in few, small portions (``knots'') of the butterfly wings. A knot may appear at either lower or higher latitudes than previous ones, in a seemingly random way; accordingly, the spot mean latitude abruptly drifts equatorward or even poleward at any knot activation, in spite of any smoothing procedure. The description, assuming that spots scatter around the ``spot mean latitude'' steadily drifting equatorward, is questioned. In a relevant number of cases, knots appear to be arranged in two roughly parallel, oblique streams, the ``spot mean latitude'' being located in the underspotted band lying between these streams.