With so many types of cells in such a small space, sometimes it is hard to tell the difference among these types of cells. Sertoli cells envelop the gamete throughout the process of development. Sertoli cells can be distinguished because they have a pale, oval-shaped nucleus with a prominent nucleolus. The nucleus is generally located midway through the cell, however, due to the plane of section, it can appear to be anywhere along the wall of the tubule. Spermatogonia are large precursor cells and are always located along the basement membrane of the tubule. Primary spermatocytes have large, heterochromatic nuclei, and they are located between the basement membrane and the lumen of the tubule. Occasionally mitotic figures can be seen in them. They do not have nucleoli.