NucleusA portion of the protoplasm within the cell is specially modified to form what is known as the nucleus. This body is usually of a spherical or oval form, and is separated from the general protoplasm (cytoplasm) by a delicate nuclear membrane. The nucleus, like the protoplasm from which it is derived, consists of hyaloplasm and an intranuclear network of spongioplasm.

The nuclear spongioplasm presents, however, a most important difference from that of the cytoplasm; it contains a number of bodies which stain very readily with certain dyes and are therefore called chromatin filaments.

The nucleus is an exceedingly important component of the cell; it cannot exist apart from the cytoplasm, while cytoplasm without a nucleus is inert and soon dies.