ABSTRACT
Mesoderm from the presumptive anlage of the limb-bud (stages 15–16 and 17 of Hamburger & Hamilton) or mesoderm from a very young limb-bud (stages 17–18) was separated from its ectoderm with trypsin or versene and grafted into the area pellucida of an embryo of 15–23 somites (stages 12–14). The mesoderm was placed in contact with the region of the somatopleure which normally gives rise to the flank of the embryo between the wing and the leg.
After the action of the trypsin solution, the mesoderm elicited the outgrowth of a supernumerary limb in only one case out of 59 (Plate 1, fig. 3).
After the action of the versene, the implanted mesoderm induced an extra limb in 22 cases out of 54 (Plate 1, figs. 4, 5, 6, 7). The inductive capacity was retained after the mesoderm had been chopped to small pieces before grafting (Plate 2, figs. 9, 10). All induced limbs grew outwards and were situated in the same plane as the limbs of the host embryo. They were all covered by host epidermis.
Control grafts of mesoderm on chorio-allantoic membrane only formed amorphous cartilaginous masses ; their development was in no case greater than their prospective value (Plate 2, fig. 11).
The host flank ectoderm, under the influence of the grafted mesoderm, formed an ectodermal ridge possessing the same properties as the ectodermal ridge of a normal limb-bud (text-fig. 1; Plate 2, fig. 14).
It is concluded that the limb-bud mesoderm is the primary inductor of the limb.
Des expériences en cours ont permis de montrer l’activité inductrice du mésoderme de la future ébauche de membre à partir du stade 20 somites.
