applyBehaviours(time, index) {
    const length = this.behaviours.length;
    let i;

    for (i = 0; i < length; i++) {
      this.behaviours[i] && this.behaviours[i].applyBehaviour(this, time, index);
    }
  }
Applies all behaviours attached to the particle.
@param {number} time The time elapsed since the last update
@param {number} index The index of the particle in its parent system