Sentence:  Particularly hard for the therapist to grasp are those instances in which the patient is manifesting an introject traceable to something in the therapist , some aspect of the therapist of which the <WSD>latter</WSD> is himself only poorly aware , and the recognition of which , as a part of himself , he finds distinctly unwelcome . 
Meaning of the word marked with <WSD> tags:  referring to the second of two things or persons mentioned (or the last one or ones of several)