The document provides instructions for labeling anatomical structures in an image related to male reproductive biology. Key features to label include the basement membrane, Sertoli cells, various stages of spermatogenesis (spermatogonia, spermatocytes, spermatids, spermatozoa), and blood vessels within the seminiferous tubule. It notes to only label present structures, omitting the tubule lumen if absent.

1. Please label the image given characteristics:
Basement membrane / basal lamina (same thing)
Sertoli cell and nucleus
Spermatogonia
Spermatocytes (primary or secondary)
Spermatids
Spermatozoa (nuclei and tails)
Blood vessel
Seminiferous tubule
Tubule lume
If it is not present no need to label