The extra finger of the chicken
In this image from the CMRB we can see the induction of an extra finger in the interdigital space of a chicken. This finger has grown thanks to a microsphere (the blue dot in the image) that is covered in Activin A, a molecule with the ability to form cartilage. The microsphere was introduced in the interdigital space of the chicken embryo when it was 5 days old. After incubating it for 3 more days, the Activin A has induced the formation of the finger.