Living Hensen's node of the definitive primitive streak of chick embryo was prepared into ‘sandwiches’ with the competent ectoderm and the sandwich grafts were transplated into the 2·5 day chick embryo using the intracoelomic grafting technique of Hamburger.

One hundred and twenty-four grafts were prepared and transplanted intracoelomically, 28 grafts were lost due to the death of the host embryos, 63 grafts did not differentiate at all, but 33 well-defined grafts were recovered, after cultivating the transplanted hosts for 12–14 days.

All kinds of tissues from feather germs to neural tissue were found to have differentiated in the grafts. The more frequently occurring tissues were feather germs, epidermal vesicle, neural tissue, kidney and muscle. Other differentiations were the cartilage notochord and gut. No definite combination pattern has emerged from the tissues. But when the tissues were traced to their germ-layer derivation, 22 of them belonged to the mesodermal complex, 11 to the ectodermal complex and 8 to the endodermal complex.

In the light of the above results, the probable existence of a mesodermal factor and an ectodermal factor independently responsible for the respective differentiations, as also the competence of the ectoderm, is discussed.

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