Photoreceptors.
I hope this helps!
Without staining them you wouldn't be able to see them
The Pancreas functions as both endocrine and exocrine.
Electrocardiograph (EKG or ECG) technicians operate equipment that measures, monitors, and graphically traces the electrical activity of the heart. Physicians use the graph (electrocardiogram/EKG/ECG) to diagnose and monitor patients' heart problems.