The cloning of a frog.

It is relatively unusual for the Nobel Prize in Physiology or Medicine to be made, to a large extent, on the basis of a single author paper, published over 50 years ago, for work carried out by a graduate student. This was largely true of a paper published in 1962 in the journal Development (called at that time the Journal of Embryology and Experimental Morphology). The main subject of that paper was the production of normal tadpoles from the nuclei of intestinal epithelium cells of Xenopus laevis. In view of this unusual situation, I have been invited to comment on the 1962 paper.