Sertoli Cells EM

This electron micrograph allows the viewer to better appreciate the microscopic structure of the Sertoli cell and blood-testis barrier. The Sertoli cell has an extensive cytoplasm and oval-shaped nucleus that contains a prominent nucleolus and extremely dense chromatin. If you look closely, a significant number of mitochondria and lipid droplets are visible outside of the nucleus, throughout the cytoplasm. The basement membrane on which all Sertoli cells rest is visible, as is a narrow myofibroblast which contracts rhythmically. The Sertoli cells are connected to one another with junctional complexes close to the basement membrane; these complexes divide the tubule epithelium into basal and adluminal comparments. The basal compartment contains diploid spermatogonia, which rest upon the basement membrane. These cells develop by migrating into the adluminal compartment, which contains primary spermatocytes, spermatids, and spermatozoa. Why are secondary spermatocytes not visible in this image?