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The Term Embryology, in its widest sense, is applied to the various changes which take place during the growth of an animal from the egg to the adult condition: it is, however, usually restricted to the phenomena which occur before birth. Embryology may be studied from two aspects: (1) that of ontogeny, which deals only with the development of the individual; and (2) that of phylogeny, which concerns itself with the evolutionary history of the animal kingdom.

In vertebrate animals the development of a new being can only take place when a female germ cell or ovum has been fertilized by a male germ cell or spermatozoön. The ovum is a nucleated cell, and all the complicated changes by which the various tissues and organs of the body are formed from it, after it has been fertilized, are the result of two general processes, viz., segmentation and differentiation of cells. Thus, the fertilized ovum undergoes repeated segmentation into a number of cells which at first closely resemble one another, but are, sooner or later, differentiated into two groups: (1) somatic cells, the function of which is to build up the various tissues of the body; and (2) germinal cells, which become imbedded in the sexual glands, the ovaries in the female and the testes in the male, and are destined for the PERPETUATION OF THE SPECIES.
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2006-09-11 00:39:00 · answer #1 · answered by Excel 5 · 0 0

"In biology, meiosis is the process that allows one diploid cell to divide in a special way to generate haploid cells in eukaryotes. Meiosis is essential for sexual reproduction. It therefore occurs in most eukaryotes, including single-celled organisms. A few eukaryotes, notably the Bdelloid rotifers, have lost the ability to carry out meiosis and acquired the ability to reproduce by parthenogenesis. Meiosis does not occur in archaea or prokaryotes, which reproduce by asexual cell division processes. In other words, meiosis is the process that produces genetic variation."

"Mitosis is the process by which a cell separates its duplicated genome into two identical halves. Mitosis occurs exclusively in eukaryotic cells. The primary result of mitosis is the division of the parent cell's genome into two daughter cells."

Is that what you meant?

2006-09-11 09:14:05 · answer #2 · answered by peter_lobell 5 · 0 0

the splitting of the cells at the process of forming a fetus.

2006-09-11 07:12:49 · answer #3 · answered by Anonymous · 0 0

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