The first sign of development in multicellular plants and animals is generally polarity: differentiation along a particular body axis, especially at its ends. Thallus pole and rhizoid pole, shoot and root poles, apical and basal poles, anterior and posterior body poles become recognizable as early landmarks at the ends of the primary axes in the various known types of organization. Even the first division of the initial cell is almost always oriented according to a major axis.
KeywordsSperm Entry Light Axis Rhizoid Cell Cleavage Wall Presumptive Ectoderm
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