الفهرس 
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Abstract
The kinetics of cellular proliferation during early rganogenesis of the head sense organs and the related parts of the brain were studied in the chick embryo of the Alexandria Egg Strain, at stages 11, 17, 20 and 25 (ages: 41-44 hours; 55-58 hours; 72-75 hours; and 108-111 hours) using colchicine as a metaphase-arresting agent. The morphological as well as the kinetic findings of this investigation indicate that: before the onset of differentiation in any of the studied regions, especially the sense organs, proliferation activity is at its highest level; and as development proceeds the differentiating regions attain lowest ,value of proliferation activity, i.e. the proliferation activity decreases as the differentiation process proceeds. The decrease in the proliferation activity depends on the lengthening of the generation time (cell cycle time) rather than the lengthening or shortening of the duration of mitosis (M-
phase) . In addition, during development the C-metaphase index can be used as an indicator of the proliferation activity, since in all the studied regions both the C-metaphase index and the J 1 proliferation activity show proportional variation with each other and pass in the same direction, more or less, parallel to each other.