SpermatoStages

A model of the seminiferous epithelium cycle

Track germ cells through spermatogenesis — forward and backward in time — across 21 species, from rat and mouse to human, bull, horse, and beyond.

SpermatoStages is an interactive teaching and research tool for reproductive biology, toxicology, and veterinary science. Pick a species, pick a cell, and predict where it will be after any number of days. Useful for identifying target cell types in toxicity studies, planning sampling, and teaching the kinetics of the cycle.

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What it does

Forward and backward prediction of germ cell positions across the cycle
Adjustable cycle length and stage frequencies per species
Stage histology images with cell labels and schematic drawings
Decision tree, manuscripts, and references built in
Runs in any modern browser — Mac, Windows, Linux, iPad, Chromebook

Built on the work of

Hess RA (1990). Quantitative and qualitative characteristics of the stages and transitions in the cycle of the rat seminiferous epithelium: light microscopic observations of perfusion-fixed and plastic-embedded testes. Biology of Reproduction 43(3): 525–542.

Hess RA, Chen P (1992). Computer tracking of germ cells in the cycle of the seminiferous epithelium and prediction of changes in cycle duration in animals commonly used in reproductive biology and toxicology. Journal of Andrology 13(3): 185–190.

About the name

SpermatoStages is the web-based continuation of a program that has been in development for nearly four decades. The earliest version was written in Turbo C for MS-DOS by Dr. Rex Hess beginning in 1988, with input from Dr. Yves Clermont (whose 1952 work with Leblond established the 14-stage system this program models). It was published as Hess & Chen 1992, rewritten for Mac by Daniel Pape in 1995, rewritten for Windows by David Scott in 2006, and now rewritten for the web as SpermatoStages in 2026. The name has been changed from STAGES to distinguish this program from other software using the STAGES name.