Donor end Host Stages 

 18 19 20 21 



22 24 



Ear Ectoderm APDD 

 to Ear Region. 

 Harrison '36a 



B. Ear Ectoderm APDD 



to Region Anterior 



to Eor 



Host Stage 22. 



Yntema '39 



0. Ear Ectoderm APDD 



to Ear Region. 



Donor Stage 20. 



Yntema, new data 



Host Stages 

 16 18 20 22 24 



Donor Stages 

 14 15 16 17 II 



. Ear Ectoderm APDD 



to Ear Region. 



Host Stages 21-23. 



Hall '39 



I. Ear Ectoderm APDD 



to Ear Region. 

 Donor Stages 21-22. 

 Hall '41 



KEY 



NOT INDICATED 



REDUPLICATION 

 ORIGINAL ASTMMEl 



Fig. 148. Differentiation of ear ectoderm placed APDD in various environments. 



A, Host and donor are at the same stage of development at the time of operation. Harmonic labyrinths 

 usually develop from grafts in which the AP axis has been rotated before fusion of the neural folds (stage 

 20) ; in operations on older stages, the labyrinths are more frequently disharmonic. 



B, The AP axis is disharmonic in the heterotopic labyrinths which have recognizable axes; at stage 14 

 the ear ectoderm may show indication of AP polarization. The site and stage used for receiving the graft 

 show no indication of reversing polarity to produce harmonic ears. 



C, The influence of the stage of the host on expression of the graft in homeotopic position is illustrated. 

 Stage 20 is more likely to produce harmonic ears from disharmonic stage 20 ectoderm than earlier or later 

 stages. The high incidence of reduplication when stage 14 is host indicates that this stage influences the 

 expression of polarity more than slightly yoxmger or older embryos. In comparison with A it is seen that 

 reduplications occurred in the stage 20 to 20 combination more frequently than in the results of Harrison. 



D, A polarity of the ear ectoderm is indicated at the beginning of neurulation which may be expressed in 

 hosts at head process stages at the time of operation. 



E, A reversal of polarity is accomplished in some cases by grafting older ear ectoderm to neurulae; as 

 shown in A, this ectoderm would more frequently develop disharmonically if grafted to hosts at the 

 stage of development as the donor. 



