EAR HELD 



OLFACTORY 

 FIELD 



TAILBUD 



TRANSPLANTED LIMB FIELD 



LARVA 



SELF-DIFFERENTIATION OF LIMB 



Fig. 44. Self-differentiation of structures in the neurula. The transplanta- 

 tion of the presumptive limb (limb field) is illustrated, together with its com- 

 plete self-differentiation in the flank region. The approximate location of the 

 presumptive ear, olfactory organ, and heart are shown in the neurula. When 

 transplanted to another embryo these regions give rise to the structures shown 

 in Figure 45. The various presumptive structures are called fields at the neurula 

 stage, and the nature of these fields is discussed in Chapter 8. The time at 

 which presumptive structures will self-differentiate when transplanted varies from 

 one structure to another. In general, mesodermal structures such as the limb 

 will self-differentiate earlier than ectodermal structures such as the eye, ear, and 

 brain. 



