. Analysis of development. Embryology; Embryology. Mesoderm. C Presumptive Presumptive Endocardium Myocardium Fig. 158. Heart localization in a tail-bud, stage 27, Amblystoma punctatum embryo. A and B, ventral and lateral views respectively; C, ventral portion of a transverse section at level indicated on B. Extirpation of all mesodermal tissue over areas outlined on A and B, extending from AT to F in section C, prevents heart formation. Extirpation of presumptive heart material, extending from Z to W in section C, prevents heart development only when the wound is filled with foreign tissue. O
. Analysis of development. Embryology; Embryology. Mesoderm. C Presumptive Presumptive Endocardium Myocardium Fig. 158. Heart localization in a tail-bud, stage 27, Amblystoma punctatum embryo. A and B, ventral and lateral views respectively; C, ventral portion of a transverse section at level indicated on B. Extirpation of all mesodermal tissue over areas outlined on A and B, extending from AT to F in section C, prevents heart formation. Extirpation of presumptive heart material, extending from Z to W in section C, prevents heart development only when the wound is filled with foreign tissue. Otherwise, mesoderm in XZ and YW areas migrates ventrad and exhibits heart potency. the existence of an inductor in the heart primordium, but other experiments have shown that the inducing activity is not lim- ited to the heart itself. It has been shown by Bacon ('45) that a normally structured heart can be organized when the heart rudiment of tail-bud stage Amblystoma is replaced with indifferent presumptive mesoderm from the marginal zone of a beginning gastrula (stage 10). The substituted tissue did not in- clude any presumptive heart material (it did not contain the lateral quadrants of the mar- ginal zone) and therefore heart self-differen- duced to form cardiac tissue when it is grown in cultixres with archenteron floor from a late neurula. The organizing power of the heart region is unable to overcome the determina- tion present in most of the mesoderm after gastrulation—at least, it is unable to induce heart from presumptive somite mesoderm from neurula stages (Bacon, '45). On the other hand, mesoderm immediately adjacent to the heart region is still competent to form heart in tail-bud stage Amblystoma embryos, as indicated in Figure 158. Is the presumptive heart mesoderm itself. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly
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Keywords: ., bookcentury1900, bookpublisherphiladelphi, booksubjectembryology
