A text-book of anatomy / edited by Frederic Henry Gerrish.

Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of anatomy / edited by Frederic Henry Gerrish. Source: Wellcome Collection.

    43/926 (page 39)
    direction. Thus is accounted for the migration of cells from blood-vessels, and their wandering from one point to another outside of the vessels. CELL REPRODUCTION. The formation of new cells is accomplished by division of old cells. The direct method, by which every element of a cell Avas equally divided by a trans- verse constriction, was formei'ly supposed to obtain generally, but is now known to be voiy rare. The indirect plan of division is almost, if not quite, universal. By this method the nucleus undergoes a series of complicated modifications, which, taken as a whole, are called kdryohinesis, a name derived from the Greek words for nut and change, the signification of the compound being the changes in the kernel or nucleus. In studying the details it is well to bear in mind that in this process, which is the principal movement toward the creation of two cells out of one, there occurs such a division of the cell-protoplasm and of the nucleus that each of the new-born cells inherits a half of every portion of the parent-cell's estate. When division is about to take place the nucleus noticeably enlarges (Fig. 9). The nuclear membrane and the nucleoli disappear, and the secondary filaments of the reticulum are drawn into the primary threads, making them thicker and more conspicuous (Fig. 10). It is not positively determined whether these threads Fig. 9.—Nucleus enlarged. The Fig. 10.—Nucleoli and second- Fig. 11.—The spindle and V body of the cell is represented ary filaments have disappeared. loops, side view. (F. H. G.) merely in outline in this series of (F. H.G.) diagrams. (F. H. G.) all unite and make one, or are separate ; whichever is true, they form a peculiar and complicated tangle which is called the skein. The diagram does not attempt to display all of the tortuosities of the skein, as they are rather confusing. There now appears a skeleton spindle 11), formed of delicate filaments of the inter- stitial substance, placed with one extremity at the pole and the other at the anti- pole. At each end of the spindle fibrils of the protoplasmic network converge and produce the appearance of rays. At the next step (Fig. 12) a number of Fig. 12.—V loops, end view. (F. H. G.) Fig. 13.—Daughter loops, end view. (F. H. G.) V-shaped loops are observed in place of the skein, these resulting either from the breaking of the single thread, on the one theory, or, on the other, from the plainer manifestation of the always separate threads. These V-shapecl pieces are short and thick, and marshal themselves aroimd the equator of the spindle, with apices to the centre and limbs outward, producing a star-like appearan(je, which is