Why it matters

Ancillon's anonymous 1707 treatise is the fullest early-modern legal and social argument over whether eunuchs and castrati could lawfully marry, weighing civil against canon law and padding the case with historical and anecdotal material; the dedication is signed with the anagram "C. d'Ollincan." Its reach extended into English through Robert Samber's translation, issued by Edmund Curll as Eunuchism Display'd in 1718, which is how the text entered the anglophone literature on castrati. It’s half treatise on castration and half gossip about opera stars.

Why we're looking

At US$318 this sits meaningfully below the two closest comps we confirmed — Justin Croft's contemporary-sheep copy at £500 and Librairie Alain Brieux's Near Fine rebound copy at US$463.03 — while being, per the seller, in a contemporary calf binding with an 18th-century armorial bookplate and a manuscript note of a 1754 sale price, which is better provenance than most copies on the market carry. Cheaper copies do exist (Livre Rare Book shows examples from about EUR 250), so this is a sensible rather than a dramatic discount.

Watch out for

The seller discloses a scratch to the upper board and a small loss at the head cap — minor, but worth seeing close photographs of the spine ends before buying. The 1707 printing exists in more than one issue of the same year with slightly differing paginations and title ornaments, per Justin Croft's description of a comparable copy, so the "sphere title" designation and the stated collation are worth confirming leaf by leaf with the seller. Nothing in the listing comments on internal condition (browning or foxing of the title and text is common in copies described elsewhere), so ask directly.