The preservation of the developmental biology film series was made possible by generous contributions from Distinguished University Professor of Geosciences, Lynn Margulis, Terence Malik, Chelsea Green Publishing, The Politics and Practice of Sustainable Living, the Hardy Lane Foundation, the International Symbiosis Society, Geo Book Studio, publisher of The Biggest Picture, hummingbird films, producer of the documentary, Symbiotic Earth, and supporters of the Lynn Margulis Archive at Scholar Works. Mameleon skin consists of a superficial epidermis and an underlying dermis. In the epidermis, dead keratinocytes make up the outer layer. Immediately below them are differentiating keratinocytes, which arise from actively dividing stem cells that lie closest to the dermis. Other cells, the melanocytes, are found among the dividing keratinocytes. These cells manufacture granules of the pigment melanin and transfer them to the keratinocytes. This diagram shows the structure of this epidermal system. The melanocytes extends long processes called dendrites between the closely packed keratinocytes in the dividing layer. Melanin granules are formed in the melanocytes and then transferred through the dendrites to the keratinocytes. When keratinocytes mature and slowly reach the surface of the skin where they die, they carry the melanin with them. This is a microscopic preparation made from a piece of guinea pig skin. The dermis has been removed with tripsin and we are looking at the basal layer of the epidermis from underneath. The specially stained dendritic melanocytes appear dark against the lightly stained keratinocytes. As the plane of focus has changed, it can be seen that melanocytes lie in different levels in the skin. To study the dynamic interactions between these two types of cells, they are isolated with tripsin and cultured in a cell suspension. Here the two cell types are easily distinguished by their shapes, but very often it is much more difficult to recognize the melanocytes. In this scene, a melanocytes develops two long dendrites, which introduce packages of pigment granules or melanocomes contained within vacuoles into a flat keratinocytes. While the individual melanocomes are too small to be seen in the light microscope, the transferred vacuoles containing many melanocomes are visible. The melanocomes are left behind as the dendritic processes start to withdraw. The vacuoles open up inside the keratinocytes, dispersing pigment into the cytoplasm. Let's watch the pigment donation again. If you have any questions, please leave a comment. Thank you. Thank you. Thank you. Thank you. Thank you.