Elementary text-book of zoology / by C. Claus ; translated and edited by Adam Sedgwick.

  • Carl Friedrich Wilhelm Claus
Date:
1889
Catalogue details

Licence: Public Domain Mark

Credit: Elementary text-book of zoology / by C. Claus ; translated and edited by Adam Sedgwick. Source: Wellcome Collection.

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    is completed when the yonng 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. Düring 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 miclear 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 (fig. 18). If the products of the division are unequal, so that the smallei- portion may be looked upon as a. production of the lai-ger, we give the name “ hudding ” to this form of reproduction. Fig. 13.—Processes of cell division in an embryonio b'.jod corpusclo of a chick (afler Bütsohli). 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 newly formed nuclei, with which the original nucleus may persist. The o\mm 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 structui'e. The Separation of groups of different cells leading to the establish- ment of varioas tissues prepares the way for the phy.siological division of labour between the Organs, which, like the tissues compos- ing them, can, according to the functions which they perform, be divided into organs of vegetative life and Organs of animal life. The former have to do with the nutrition and maintenance of
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