As previously described, you can clearly see three stages of 4-to-1 Multiplexers with the smaller 2-to-1 Multiplexers in front of every stage.  Also, pay close attention to the outputs at each stage.  At each output on the 4-to-1 Multiplexers, a bit is directed either left or right depending upon whether the  SHIFT signal is set to '1' or '0' (1 = right, 0 = left).  For instance, at the output of the second stage, the bit is directed either one place to the right or left since the last stage is only shifting one place.   Thus, each stage shifts N bits left or right if its shift amount is N.  The AND gate, used for Arithmetic Shifting, is clearly shown connected to only the first four Multiplexers of the first stage.