192 



organisers: inducers of differentiation 



A fact of great importance is that the various determinations are 

 regional, but the regions are not very closely circumscribed. There 

 is as it were a certain amount of latitude as to exactly where a 

 particular structure will arise, although it is bound to be within 



Fig. 91 

 Diagram showing the results of grafting portions of presumptive epidermis or 

 presumptive neural plate from a gastrula into various regions of the flank of a 

 neurula (Triton). The grafts are induced to undergo differentiation into the 

 structures enumerated in the left-hand column ; the effect of the position of the 

 graft in the host upon the type of structure resulting is indicated by the extent 

 of the lines in the right-hand column, imagined as projected on to the larva shown 

 above. (From Holtfreter, Arch. Entwrtiech. cxxvii, 1933.) 



a certain region. The following table will show the frequency with 

 which particular structures are induced from ectodermal grafts in 

 different parts of the body : 



