Arrows and archery are directly mentioned in an ardilous letter, by married Ada, to Van:

"I have just read Reflections in Sidra, by Ivan Veen, and I regard it as a grand piece, dear Professor. The ‘lost shafts of destiny’ and other poetical touches reminded me of the two or three times you had tea and muffins at our place in the country about twenty years ago. I was, you remember (presumptuous phrase!), a petite fille modèle practicing archery near a vase and a parapet and you were a shy schoolboy (with whom, as my mother guessed, I may have been a wee bit in love!), who dutifully picked up the arrows I lost in the lost shrubbery of the lost castle ..."  - should we remember that Darkbloom explains further on ( "The direction of Time, the ardis of Time, one-way Time...") that, on p.430, the word "Ardis" means "arrow."

 

In French arrow is translated as "flèche," also used by the siblings as an echo to the English word "flesh," suggesting a symbolic meaning for "arrow" (now, "verge"*)  as in: "With the return of health the image of Ada kept rising within him like a bitter and brilliant wave, ready to swallow him...a special vest-like affair of flannel enveloped his torso, and though it was tight and thick it did not protect him any longer from the poisoned point of Ardis. Arrowhead Manor. Le Château de la Flèche, Flesh Hall."

 

However, a third possibility lies when we link the fleshy arrow mentioned as the "poisoned point of Ardis," with the Greek word "toxon," **  to confirm Nabokov's familiarity with its original meaning (arrows and poison), something rather confusing for it's extremely difficult, for me, to distinguish his multiple alusions.

After all, when is the author playing with words, metaphors, puns or etymology ( i.e., when does he point towards actual "poisoning," when is this dangerous toxin  only an indication of the "sore roses of eros," or of passion? ). We also know that the author suffered from psoriasis (which erupted more strongly once, after he broke off with his lover, Irina) why is there such a cruel mockery of the diminute librarian, Mr. Verger?  

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* - "Ada showed Van a letter from Dr Krolik on the same subject; it said (English version): ‘Crimson-blotched, silver-scaled, yellow-crusted wretches, the harmless psoriatics (who cannot communicate their skin trouble and are otherwise the healthiest of people — actually, their bobo’s protect them from bubas and buboes, as my teacher used to observe) were confused with lepers — yes, lepers — in the Middle Ages, when thousands if not millions of Vergers and Vertograds crackled and howled bound by enthusiasts to stakes erected in the public squares of Spain and other fire-loving countries.’ But this note they decided not to plant in the meek martyr’s index under PS as they had first intended: lepidopterists are over-eloquent on lepidosis." All the time its seems to me there's a strange play around a psoriatic Mr.Verger, who leaves scattered white fluff all over the place, and the French word "verge", also used in Ada's message to Van: