. Analysis of development. Embryology; Embryology. Heart, Blood Vessels, Blood, and Entodermal Derivatives 443 dependent upon a secondary entodermal in- ductor for its differentiation? Nieuwkoop ('46) found an absence of the heart in Triton embryos which developed after complete removal of the entoderm from early neurula. Bacon (personal communication) has ob- tained similar results for Amblystoma oper- ated upon at Harrison's stages 15-18, and Balinsky ('39) has reported similar findings for nevirula stage Tritons. One finds it diffi- cult to explain the lack of heart development in entoderml
. Analysis of development. Embryology; Embryology. Heart, Blood Vessels, Blood, and Entodermal Derivatives 443 dependent upon a secondary entodermal in- ductor for its differentiation? Nieuwkoop ('46) found an absence of the heart in Triton embryos which developed after complete removal of the entoderm from early neurula. Bacon (personal communication) has ob- tained similar results for Amblystoma oper- ated upon at Harrison's stages 15-18, and Balinsky ('39) has reported similar findings for nevirula stage Tritons. One finds it diffi- cult to explain the lack of heart development in entodermless embryos in view of other evidence favoring ability of very early stages for cardiac self-differentiation. Heart Determination and Self-Differentia- tion. The first experimental evidence indi- cating the stage from which the presumptive heart-field can self-differentiate into an or- ganized heart was obtained by Ekman ('21). Using Bombinator embryos at the stage when the heart is first visibly indicated, he ex- planted the heart primordivim in an ecto- dermal covering. Using similar methods and materials, Stohr ('24a) concluded that the heart differentiation in the explants was correlated with the presence of neigh- boring entodermal and mesodermal cells re- moved with the heart. Further evidence on the problem has been obtained from both explantations (Ekman, '24, '27, '29; Bacon, '45) and heterotopic transplantations (Stohr, '24b; Copenhaver, '26). The former method permits a study of heart formation free of confinement and association with other tis- sues; the latter method permits a study of the organ freed only from the structures with which it is normally associated but it gives more differentiation than the isolation method and enables one to identify the dif- ferent heart chambers with more assurance. Stohr's results with this method reempha- sized his belief in the importance of "Endo- mesodermzellen" which were always present in successful transplants. On
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Keywords: ., bookcentury1900, bookpublisherphiladelphi, booksubjectembryology
