SPERMATOGENESIS
ACT 01 · THE ORGAN
250 metres of tubule in a 12 gram package
The geometry here is built from measured dimensions, not scanned — the same as /gestation and for a related reason. BodyParts3D does carry a testis, but as a closed outer surface with no interior, and the interior is the whole subject: a testis that is a smooth ellipsoid tells you nothing, and the point is that there are 250 metres of tubule inside it.
where these numbers come from
Organ dimensions and the vascular anatomy from Gray's Anatomy (41st ed.). Reference values from the WHO laboratory manual for semen analysis, 6th ed. (2021) — those are 5th-centile figures from men whose partners conceived within a year, not targets. The 74-day cycle and the production rate from Amann (J Androl, 2008), and the original human staging from Heller & Clermont (Science, 1963).
The geometry is built rather than scanned. BodyParts3D does carry a testis, but as a closed outer surface with no interior — and the interior is the whole subject here. A testis drawn as a smooth ellipsoid tells you nothing; the point is that there are about 250 metres of tubule inside it.