Tadpole head. Front view of the head of a common frog tadpole (Rana temporaria), showing its gills (frond-like, lower left and right). This is the external gill stage. The gills are feathery and present a large surface for the uptake of oxygen. The head also shows the eye pits (dark spots, centre left and right) and mouth (centre). The tail (upper right) can be seen extending out behind the body. Magnification: x15 when printed at 10 centimetres wide.