A number of observers have studied the effects of partial or total extirpation of the limb buds of various embryos. Also, the transplantation of limb buds has been successfully carried out in connection with various problems. Byrnes, in 1898, studied the regeneration of limbs in Rana embryos after extirpation of the limb rudiments and found that if the region in which the hind limb developed is destroyed, a limb nevertheless develops out of the tissue which moves in from the periphery and covers the wound. Braus ( '06) found that the hind-limb region of Bombinator, as well as Rana, is much more capable of regeneration than the fore-limb region. He showed, in his own experiments on the regeneration of the fore-limb of Rana embryos, that only the shoulder-girdle and some of its muscles are formed after removal of the limb bud, unless the operation is done at a comparatively early stage, in which case the regeneration of the whole extremity may take place. Harrison ( '18), experimenting on the fore-limb of Amblystoma punctatum, found that extirpation of the tissue in the region of the rudimentary limb bud results in a ldlisturbance of the development of the limb, the intensity of which depends upon the size of the wound, the care with which the mesodermal cells are cleared away, and whether o r not the wound is 'This work was started in the Anatomical Laboratories at the University of Missouri in 1920 and coiiipletcd in the Anntomical Laboratories of the Hnr\nrd Mtdieal School in 1922.