appendTurtles = g => {
g
.append('defs')
.append('g')
.attr('id', 'dart')
.append('polygon')
.attr('points', '0.5,0, -0.5,0.4, -0.25,0, -0.5,-0.4')
.attr('transform', `scale(${turtleSize})`)
.attr('vector-effect', 'non-scaling-stroke')
.attr('style', 'stroke: black; stroke-width: 1px')
g
.selectAll('.dart')
.data(model.turtles)
.enter()
.append('use')
.attr('xlink:href', '#dart')
.attr('style', d => `fill: ${randomColor()}`)
}