Letter 38 of July 16, 1683 Figure 1 | Arcana Naturae Microscopiorum

Little animals, moving and dead, both from the testicles and from the carrying-away seed vessels of the frog.
Dierkens, beweegde en doot, uijt de testicullen als afdragende zaad-vaten van de kikvors.
The scientists who edited the early volumes of Alle de Brieven / Collected Letters translated as afdragende zaad-vaten as "deferent ducts".