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Why does the total volume of an embryo change little during cleavage?
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Animal development
The embryos of many animals appear similar to one another in the earliest stages of development and progress into their specialized forms in later stages.
During the process of cleavage, the total volume of an embryo changes little because there is almost no growth occurring between consecutive cell divisions.12
Instead of increasing in size, the zygote undergoes a series of rapid mitotic divisions that subdivide the existing cytoplasm into smaller cells known as blastomeres. Because the total mass of living substance does not increase during this period, the size of the individual cells is reduced by approximately half with each successive division. This rapid subdivision allows the embryo to produce a large number of cells of a more conventional size, which serve as the early building units for the future organism.12