Sentence:  A study of their activity on thyroglobulin has shown that thyroxine is not preferentially released and that the degradation <WSD>proceeds</WSD> stepwise with the formation of macromolecular intermediates ( Alpers , Petermann and Rall , 1956 ) . 
Meaning of the word marked with <WSD> tags:  move ahead; travel onward in time or space