. The physiology of the domestic animals; a text-book for veterinary and medical students and practitioners. Physiology, Comparative; Domestic animals. 16 PHYSIOLOGY OF THE DOMESTIC Fig. 4.—Blood-Corpuscles in Different Stages of Development, showing Reproduction by Fis- sion. (Ranke.) (the blastema), forming the so-called " free cell-formation," or by the subdivision of a previously-existing cell,—the " endogenous cell-forma- ; According to the first of these views, which may be compared to the formation of crystals in a saline solution, granules first devel
. The physiology of the domestic animals; a text-book for veterinary and medical students and practitioners. Physiology, Comparative; Domestic animals. 16 PHYSIOLOGY OF THE DOMESTIC Fig. 4.—Blood-Corpuscles in Different Stages of Development, showing Reproduction by Fis- sion. (Ranke.) (the blastema), forming the so-called " free cell-formation," or by the subdivision of a previously-existing cell,—the " endogenous cell-forma- ; According to the first of these views, which may be compared to the formation of crystals in a saline solution, granules first develop in a fluid which contains all the chemical constituents of the organism, forming the nucleolus of the future cell. Around this other granules are gradually deposited until the nucleus is formed, and the cell-contents and membrane gradually consolidate around this. The first objection to this theory, which, it is seen, implies spon- taneous generation, lies in the fact that no one has ever been able to demonstrate such a cell- formation or to discover the so-called cyto- blasts. It was then shown that all the cells of the embryo originate in the segmentation spheres of the ovum, and the falsity of this doctrine of free cell- formation is further proved from analogy by the manner in which the connective-tissue cells take part in the development of pathological new formations. There is now no more firmly-established dictum in physi- ology than the statement that every cell originates from a previously- existing cell. (Omnis cellula e cellula.) The other view, which was also to a certain extent advocated by Schwann, as to the origin of cells by sub- division of a parent cell, is exemplified in the mode of reproduction of many of the lower forms of life. Cells may reproduce themselves by simple division of the parent cell or by endogenous division. Cell reproduction always starts in the nucleus. In simple division the nucleus first becomes marked with a furrow, which grad- ua
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