in 12 month old animals , a few sertoli cells exhibiting the vesicular elements appeared in the nucleolar region while in animals over 15 months of age sertoli cells could be positively identified by the characteristic cytoplasm containing microtubules , elongated and electron dense mitochondria , extensive granular endoplasmic reticulum and the presence of spermatids in various stages of spermiogenesis .
C0010834
cytoplasm
C0230779
granular endoplasmic reticulum