g){
  // create the circle
  var circleRadius = core.randi(13,20);
  // change circle color for additional variation.
  var circleColor = core.sample(['blue', 'red', 'black', 'green', 'yellow', 'orange', 'white']);
  var generatedCircle = { cx: core.randi(20+circleRadius,140-circleRadius), cy: core.randi(20+circleRadius,
    100-circleRadius), r: circleRadius, stroke: 'black', fill: circleColor, class: 'black-circle' };
  shapes.drawCircles([ generatedCircle ], svg);
  d3.selectAll('circle').call(shapes.dra