Kirkes' handbook of physiology. / By W. Morrant Baker and Vincent Dormer Harris.
- William Senhouse Kirkes
- Date:
- 1888
Licence: Public Domain Mark
Credit: Kirkes' handbook of physiology. / By W. Morrant Baker and Vincent Dormer Harris. Source: Wellcome Collection.
Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.
33/912 page 9
![protoplasm each containing a nucleus (fig. 4, b). Tliis jDrocess 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-cells of many animals. In some cases (fig. 5), the process Fig. 5.—lilood-coi-pimde from a young deer embr;/o, 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 occiu'S, I'endering 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 Fig. 6.—Diiii/rnm of a mrtilin/r, cell inider/jniiii/ Jinsiiiii within itn eii/iniile.—Tlie proccsH of division is represented as commencing in the nucleoluH, extending to the nucleus, and at length involving the body of the cell. (Frey.) cases there is a primary fission into three instead of tlie usual two cells. In cartilage (fig. 6), a process essentially similar opcurs, with the exception that (as in the ovum) the cells ])ro(lucerl by fission remain in the original capsule, and in tiicir turn undergo division, 80 that a large number of cells are sometimes observed within a common envelope. Tiiis i)rocess of fission within a capsule has](https://iiif.wellcomecollection.org/image/b24757226_0033.jp2/full/800%2C/0/default.jpg)
