be ploughed defined by the rearward projection or track between the outermost edges 104 106 of the plough blade continues to coincide with the tracks of the wheels 80 82 fig9 shows the body when rotated fully in the opposite direction i e with the cylinder 100 fully extended and the plough in a right displacing configuration now the shape of the quadrilateral 92 94 96 98 has distorted in the opposite manner relative to the fig7 shape with the distal axes of rotation and hence the apparatus body 52 shifted to the vehicle 39 s left i e as the body rotates clockwise the first and second pivot arms 74 76 rotate counter clockwise about their proximal axes of rotation 92 98 it can again be seen that this has the effect of keeping the track defined between the plough blade edges 104 106 aligned with the track of the wheels 80 82 when the vehicle drives straight ahead it is noted that as shown in fig8 and 9 the castors 68 have not rotated to trail along the line of the direction of travel as they would in fact do if the apparatus was driven in contact with the ground fig1 and 11 show the arrangement of fig7 from either side i e the front of the vehicle 78 with its pick up and mounting structure 88 in engagement with the apparatus 39 s vehicle mounting 70 it can be seen in this view that arm 74 is in two sections 74 a and 74 b section 74 a extends rearwardly from the first distal axis of rotation or pivot point 94 over the top of the vehicle body 52 and section 74 b connects downwardly at an angle to the first proximal.