What metaphors are used in The English Pupil by Andrea Barrett?

The erosion of Linnaeus' memory is conveyed by a metaphor of a gradually expanding dark lake: His mind, which had once seemed to hold the whole world, had been occupied by a great dark lake that spread farther every day and around which he tiptoed gingerly. Similarly, the facts that were once at his command now "darted like minnows across the water and could only be captured by cunning and indirection."