Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 CELL DIVISION. 31 is completed when the young nuclei, proceeding from the two poles of the nuclear spindle and the surrounding clear protoplasm, have attained their definite size, and the remains of the fibres have been absorbed. During these processes the protoplasm of the cell has gradually become more and more constricted by a furrow which is directed transversely to the long axis of the nuclear spindle, and which after the completion of the division of the nucleus brings about a sepa
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 CELL DIVISION. 31 is completed when the young nuclei, proceeding from the two poles of the nuclear spindle and the surrounding clear protoplasm, have attained their definite size, and the remains of the fibres have been absorbed. During these processes the protoplasm of the cell has gradually become more and more constricted by a furrow which is directed transversely to the long axis of the nuclear spindle, and which after the completion of the division of the nucleus brings about a separa- tion of the cell contents into two masses—the daughter cells (%%%%%%%%%%%%%%%%• 18). If the products of the division are unequal, so that the smaller portion may be looked upon as a production of the larger, we give the name ' budding ' to this form of reproduction. FIG. 18.—Processes of cell division in an embryonic blood corpuscle of a chick (after Biitscbli). K, nuclear spindle. Kp, nuclear plate or equatorial thickening-. Finally, the term endogenous cell formation is applied to that method of increase in which the cells originate within the mother- cell. In this case the protoplasm does not divide by a progressive constriction and separation into two or more parts, but differentiates itself round the neAvly formed nuclei, with which the original nucleus may persist. The ovum which we have to contemplate as the starting-point of the development of the organism produces by these various methods of cell multiplication the material of cells which serves for the for- mation of the tissues. Groups of originally indifferent and similar cells break up and assume severally a changed appearance. The constituent elements undergo various differentiations, and from them and their derivates is produced a definite form of tissue, endowed with a function corresponding to the peculiarity of its structure. The separation of groups of different cells leading to the establish- me
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