call on the manesThe Oxford English Dictionary nicely captures the rationale for Victor's use of this Latinism, defining the term in the plural, as
the deified souls of departed ancestors (as beneficent spirits; opposed to larvæ and lemures, the malevolent shades of the Lower World). Also, the spirit, `shade' of a departed person, considered as an object of homage or reverence, or as demanding to be propitiated by vengeance.The manes Victor lists here have in the aggregate constituted the guiding spirits that throughout this chapter he has invoked as demanding his intercession to avenge their deaths. Upon his own death he foresees himself joining their number. If Walton is expected to pick up the family cause, perhaps in thinking of Victor as "the brother of [his] heart" (I:L4:22) he has got much more than he bargained for.