code: function( options ){
  
              var self = this;
              // call parent init method
              parent.init.call(this, options);
  
              this.options.defaults( defaults );
              this.options.onChange(function( opts ){
                  this.radius = opts.radius;
              });
              this.options( options );
  
              this._aabb = Physics.aabb();
              this.radius = this.options.radius;
          }
docs: extended