Nucleus

It is mostly rounded or elliptical but may be of other shapes also. It is surrounded by a two layered membrane, the nuclear membrane, which is providedwith very fine pores. Inside the membrane is the liquid phase the nuclear sap or karyolymph in which is embedded a network of fine threads called chromosomes. On the chromosomes, are present minute regions called genes. The chromosomes are chemically composed of four kinds of molecules:

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