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INDUCTION AND ORGANISATION 



material that comes within its reach. Such material then 

 acquires the power of organisation, and can thenceforward act 

 as an organiser itself (Spemann and Geinitz, 1927). A piece 

 of prospective ectoderm from one early gastrula, grafted into 

 the dorsal lip of the blastopore of another, will in 24 hours 



Fig. 45. Diagram of operation, (a) part of the presumptive ecto- 

 derm, of an early gastrula is (b) grafted into the dorsal lip of the 

 blastopore of another germ of the same age. After 24 hours, (c), 

 part of the graft has already been rolled in over the edge of the 

 host's blastopore. The part that is not yet rolled in is now removed, 

 and (d) grafted into the ventral side of a third gastrula. 



acquire all the properties of blastopore lip material. If removed 

 again, and grafted into the ventral side of a third embryo 

 (Fig. 45), it will first of all prove to have acquired the topo- 

 genetic capacity of independent invagination, followed by 

 differentiation into notochord and somites. Moreover, it has 

 become an organiser which gives rise to the primordium of 

 a secondary embryo at the place of implantation (Raven, 



