Hand-book of physiology / by W. Morrant Baker and Vincent Dormer Harris.

  • William Morrant Baker
Date:
1888
Catalogue details

Licence: Public Domain Mark

Credit: Hand-book of physiology / by W. Morrant Baker and Vincent Dormer Harris. Source: Wellcome Collection.

    33/910 (page 9)
    protoplasm each containing a nucleus (fig. 4, h). This process being repeated by the formation of a second furrow at right angles to the first, we have four cells produced (c): this subdivision is carried on till the ovum has been divided by segmentation into a mass of cells (mulberry-mass) (d) out of which the embryo is developed. Segmentation is the first step in the development of all the higher animals, including man. Multiplication by fission has been observed in the colourless blood-cel]s of many animals. In some cases (fig. 5), the process Fig. 5.—Blood-corpuscle from a young deer emhrrjo, multiplying by fission. (Frey.) has been seen to commence with the nucleolus which divides within the nucleus. The nucleus then elongates, and soon a well- marked constriction occurs, rendering it hour-glass shaped, till finally it is separated into two parts, which gradually recede from each other: the same process is repeated in the cell-substance, and at length we have two cells produced which by rapid growth soon attain the size of the parent cell {direct division). In some Eig. 6—Diagram of a cartilage cell undergoing fission loithin its capsule.~The process of division is represented as commencing in the nucleolus, extending to the nucleus and at length involving the body of the cell. (Frey.) ' cases there is a primary fission into three instead of the usual two cells. In cartilage (fig. 6), a process essentially similar occurs, with the exception that (as in the ovum) the cells produced by fission remain in the original capsule, and in their turn undergo division, so that a large number of cells are sometimes observed within a common envelope. This process of fission within a capsule has