. "'7 is a perspective view of the lower portion of the mechanisms of said unit; Figures 8A, 8B and 8C are views of one of the mechanisms of the selector unit in the positions of rest, active and passive operation; Figures 9A and 9B are a perspective and a front view, respectively, of a mechanism for the identification and extraction as used in such units; Figure 9C is a perspective view of an elemen" . . .