And as these caroteneocides progress, as they begin to secrete produce our carotene, they begin to move up along the epidermis. So eventually they move up into this section, which is the Stratum spinosum. So these rat cells are basically the living keratinocytes. Now the keratinocytes continue to move up along the epidermis and as they move deeper and farther up along the epidermis, they slowly begin to die off. And that's because the epidermis doesn't actually contain any blood vessels. And that means as the keratino sides move higher up, they cannot actually obtain the nutrients needed to actually continue living.