ABSTRACT
Fragments of Hensen’s node or head process were implanted into the primitive streak 0·8 mm behind the node. The posterior region was isolated from all influences emanating from the anterior part of the blastoderm, either by cutting off a large rectangular piece just in front of the implant or by explanting the region combined with the notochord implant into the area opaca. As controls, corresponding regions of the primitive streak were isolated or explanted.
In controls, somite formation never took place, while the implantation of presumptive notochord into this posterior region was followed by the formation of somites in most cases.
In these experiments, the action of the presumptive notochord in its new situation was similar to that of the chorda-factor in amphibians.
