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An analysis of the early development of the chick by means of the mitotic index
Author(s) -
Derrick G. Ethel
Publication year - 1937
Publication title -
journal of morphology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.652
H-Index - 74
eISSN - 1097-4687
pISSN - 0362-2525
DOI - 10.1002/jmor.1050610203
Subject(s) - biology , primitive streak , anatomy , ectoderm , somite , embryo , mitotic index , mesoderm , neural plate , neural tube , mitosis , embryogenesis , microbiology and biotechnology , embryonic stem cell , gastrulation , genetics , gene
Using the percentage of mitotic figures in the cells as an index, a study was made of the distribution of cell multiplication in the development of the chick embryo. Counts were made of all regions in embryos ranging from the embryonic shield stage to sixteen somites, and of the neural and sensory epithelia and axial mesoderm of older embryos. Figures are presented which are believed to establish the sufficiency of mitotic division in producing the cell increases in the early embryo. In the developing primitive streak, areas of superior division rate were found in the presumptive medullary plate ectoderm at the sides of the streak. The node and the primitive plate tend to exhibit lower rates than the axis of the streak. The posterior nerve cells multiply more rapidly than the average of the neural tube, and areas of activity in the mesoderm tend to be located near the posterior end. An antero‐posterior gradient of the index is indicated in the anterior neural tube, meeting a transient postero‐anterior gradient of the hinder cord in the yolk‐sac region. A lower rate of division in the floor than in the sides of the neural ectoderm may be implicated in the inrolling of the medullary plate and in the ventral ourvature of older embryos. All indices drop progressively with advancing age and differentiation.