Chick embryo showing the developing skeleton

A 13-day old chick embryo that has been stained to highlight the skeleton. The blue stain shows cartilage, while the red indicates areas that have started to form bone. The other tissues have been partly dissolved by chemicals to show this more clearly. The row of blue rings in the neck shows the cartilage rings of the trachea (windpipe). This image is a photograph taken with a macro lens and lit from behind. The embryo is about 35mm in length.

Professor Ruth Bellairs and Dr Jeremy Cook, Department of Anatomy and Developmental Biology, University College, London.