the ultrastructural study of nucleoli and ribonucleoprotein-containing structures in human seminiferous tubules revealed that the nucleoli of spermatogonia , spermatocytes and sertoli cells exhibited a tripartite structure consisting of : a fibrillar center , a compact granular portion , and a reticular portion containing both pars fibrosa and pars granulosa .
C0036630
structures
C0037863
spermatocytes