Definition of "spermist"

Esa-Pekka Salonen, in his wry program notes for his “Homunculus” (2007) for string quartet, writes that he has long “been fascinated (and amused) by the theory of the arcane spermists, who held the belief that the sperm was in fact a ‘little man’ (homunculus) that was placed inside a woman for growth into a child.”

2009 March 27, Vivien Schweitzer, “Night of New York Debuts, and a Farewell”, in New York Times‎