Ear and Nose 



421 



'39). A developmental dependence of the ear 

 vesicle upon the hindbrain is shown by ex- 

 plantation experiments in Rana and Bufo 

 (Guareschi, '35), and in Triton (Mangold, 

 '37); it is also implied when auditory vesi- 

 cles occur along with induced neural tis- 



neural tube is associated with induction of 

 the ear. 



The normal inductors of the ear are not 

 species specific in Amphibia (Holtfreter, 

 '35; Albaum and Nestler, '37; Schmidt, '38; 

 Kogan, '39). Ears indviced xenoplastically 



Fig. 150. Fig. 151. 



Fig. 150. Three-dimensional graph indicating the normality of ears induced from gill ectoderm grafted 

 into the ear region. The two horizontal axes are determined by the duration of stages at a given tempera- 

 ture; the vertical axis represents the normality of labyrinths induced from various combinations of donor 

 and host stages. 



The view indicates primarily the results obtained when older donors are used with hosts ranging from 

 yolk-plug to motile stages (stages 12 to 35). The peak of the graph represents the normal response of the 

 stage 12 to 12 combination; no other combination of stages consistently produced normal labyrinths. The 

 two ridges labelled A and B represent periods of maximal activation at stages 14 and 20, respectively. The 

 normality of vesicles falls off as hosts and donors become more developed. 



Fig. 151. Another aspect of the graph, showing the more complicated results which are produced when 

 younger donor stages are used. The face of the wall labelled C indicates the acquisition of competence to 

 respond to neural activation by stage 18 gill ectoderm. The wall to the right of the label D indicates a 

 marked rise by stage 13 ectoderm in competence to respond to mesodermal activation. The ridges to the left 

 of these walls separated by a shallow recession represent the stages of maximal competence; D indicates the 

 period of maximal competence to respond to mesodermal activation — stage 13; C indicates the same for 

 neural activation — stage 18. 



The region E represents negative results obtained by placing ectoderm lacking neural competence on 

 older hosts. The region F represents combinations in which tissue of the central nervous system is induced 

 with or without associated ear vesicles. Since ear vesicles alone did not form, the ability to produce ears was 

 not measured. 



sue, e.g., Triton (Holtfreter, '35). The re- 

 sults of Trampusch ('41) with Ambly stoma, 

 and Barbasetti ('48) with Rana indicate 

 that migrant nem-al crest cells may induce 

 ear formation. If these cells are a part of 

 the normal induction system they may aug- 

 ment activation by the rudiment of the hind- 

 brain itself. Experiments on Acipenser 

 (Ginsberg and Dettlaff, '44) and the chick 

 (Waddington, '37) also indicate that the 



may become functional (Andres, '45) and 

 their rate of development is characteristic of 

 the donor species (Andres, '49). The results 

 of Woerdeman ('38) show that urodele optic 

 vesicle or fibers arising from its retinal 

 layer can serve as an abnormal inductor for 

 ear formation. Other specific abnormal in- 

 ductors of the ear may well be found, as is 

 implied by the work of Chuang ('39) and 

 Toivonen ('40). 



