Final answer:
Lymphocytes are the large purple-stained cells with a single nucleus often seen in anatomy. They are a type of white blood cell that plays a crucial role in the immune system.
Step-by-step explanation:
The purple-stained spherical cells with a single often large nucleus occupying much of the cell's volume are called lymphocytes. Lymphocytes are white blood cells that are an important part of the immune system. They come in two main types: B cells and T cells, with the latter divided into small and large variants.