. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative. 158 COMPARATIVE PHYSIOLOGY. The History of the Blood-Cells. "We have already seen that the Ijlood and the vessels in â which it flows have a common origin in the mesoblastic cells of the embryo chick ; the same applies to mammals and lower groups. The main facts may be grouped under two head- ings : 1. Development of the blood-corpuscles during embry- onic life. 2. Development of the corpuscles in post-embryonic life. The origin and fate of the corpuscles,
. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative. 158 COMPARATIVE PHYSIOLOGY. The History of the Blood-Cells. "We have already seen that the Ijlood and the vessels in â which it flows have a common origin in the mesoblastic cells of the embryo chick ; the same applies to mammals and lower groups. The main facts may be grouped under two head- ings : 1. Development of the blood-corpuscles during embry- onic life. 2. Development of the corpuscles in post-embryonic life. The origin and fate of the corpuscles, especially of the colored variety, have been the subject of much discussion. The best established facts are stated in the summary below, while they are illustrated by the accompanying fig- ures. The colorless cells of the blood first arise as migrated undifferen- tiated remnants of the early embryonic cell colonies. That they re- main such is seen by their physiological be- havior, to be considered a little later. Afterward they are chiefly pro- duced from a peculiar form of connective tis- sue known as leucocy- tenic, and which is gathered into organs (lymphatic glands), the chief function of which is to produce these cells, though this tissue is rather widely distributed in the mammalian body in other forms than these. Summary.â^The student may, with considerable certainty, consider the colorless corpuscle of the blood as the most primi- tive; the red, derived either from the white or some form of more specialized cell; the nucleated, as the earlier and more youthful form of the colored corpuscle, which may in some groups of vertebrates be replaced by a more specialized (or de-. FiQ. 143.âSurface view from below of a email por- tion of posterior end of pellucid area of a chick of tliirty-six hours, 1 x 400 (Foster and Balfour). J. c, blood-corpuscles ; a, nuclei, which subse- quently become nuclei of cells forming walls of blood-vessels; j). pr, protoplasmic processes, con
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