Etude des duplications encéphaliques chez l’embryon de Poulet par implantation de mésoderme ventral présomptif

Study of the encephalic duplications produced in the chick embryo by implantation of presumptive ventral mesoderm in the node area Material from the posterior third of the primitive streak has been implanted in place of Hensen’s node or in its close vicinity. Implants of embryonic haemopoietic tissues were also used as well as inert material (agar) for controls. The replacement of Hensen’s node by yet-undifferentiated material (even lateral to the streak) leads to encephalic twinning. The implantation of the same material in a paraxial location leads to various results extending from normal cephalogenesis to encephalic twinning. There is no effect from the same material when implanted in front of Hensen’s node or behind it, nor is there an effect from other materials when implanted into the node. It is concluded that the ventral material leads to twinning owing to its ability to participate in the morphogenetic movements of the neighbouring territories, while modifying them, and to form dorsal structures under their influence.