1. A technique for the grafting of cortical material from one embryo to another at early cleavage stages is described. This method may also be used for the grafting of cortical material from infertile eggs to early cleavage stages.

  2. Grafts transplanted to embryos during first cleavage to the same site as that from which they were derived, resulted in normal development. Grafts obtained from grey crescent material and transplanted to the ventral margin induced the appearance of a secondary dorsal lip and subsequent secondary axis. Those of animal pole or ventral margin material placed in the grey crescent resulted in the failure of invagination during gastrulation at the graft site, and this causes the splitting of the dorsal lip into two and the appearance of double axes. Animal pole material placed at the vegetal pole produces a peculiar form of exogastru-lation.

  3. Cortical material from infertile eggs if grafted into embryos during their first cleavage inhibits further development. Cortical material from fertile uncleaved eggs, if placed in embryos in the midst of their first cleavage, appears to cause a lag in cleavage in that half of the embryo which received the graft.

  4. These results show that the cortical material definitely possesses morphogenetic properties which may be transferred with it. These are concerned with gastrulation, and the experiments are discussed in relation to the ‘cortical field’ theory of Dalcq & Pasteels. This technique of grafting allows investigation of the organization of the cortical field.

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