. Analysis of development. Embryology; Embryology. 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 13 14 16 Donor Stages 18 20 1 22 24 1 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 m 9 ^ TTO m I. Ear Ectoderm APDD to Ear Region. Donor Stages 21-22. Hall '41. KEY NOT INDICATED REDUPLICATION ORIGINAL ASTMMEl Fig. 148. Differentiation of ear ecto
. Analysis of development. Embryology; Embryology. 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 13 14 16 Donor Stages 18 20 1 22 24 1 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 m 9 ^ TTO m 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;
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Keywords: ., bookcentury1900, bookpublisherphiladelphi, booksubjectembryology
