File:The cell in development and inheritance (1902) (14760144066).jpg

Identifier: cellindevelopmenwils2 (find matches)
Title: The cell in development and inheritance
Year: 1902 (1900s)
Authors: Wilson, Edmund B. (Edmund Beecher), 1856-1939
Subjects: Cell Physiological Phenomena Cells
Publisher: New York : Macmillan
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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ater stages of development; both haveessentially the same structure and both may have the same power ofdevelopment, for there are many cases in which a small fragmentof the body consisting of only a few somatic cells, perhaps only ofone, may give rise by regeneration to a complete body. The dis-tinction between somatic and germ-cells is an expression of the ^ Parthenogenesis, p. 3, 1849.2 Arch. Mik. Anat., XVIIL, p. 112, 1880.122 THE GERM-CELLS 123 physiological division of labour; and while it is no doubt the mostfundamental and important differentiation in the multicellular body,it is nevertheless to be regarded as differing only in degree, not inkind, from the distinctions between the various kinds of somatic cells.In the lowest multicellular forms, such as Volvox (Fig. 57), thedifferentiation appears in a very clear form. Here the body consistsof a hollow sphere, the walls of which consist of two kinds of cells.The very numerous smaller cells are devoted to the functions of nutri-
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Fig. 57.— Volvox, showing the small ciliated somatic cells and eight large germ-cells (drawnfrom life by J. H. Emerton). tion and locomotion, and sooner or later die. A number, usually eight,of larger cells are set aside as germ-cells, each of which by progressivefission may form a new individual like the parent. In this case thegerm-cells are simply scattered about among the somatic cells, and nospecial sexual organs exist. In all the higher types the germ-cellsare more or less definitely aggregated in groups, supported and nour-ished by somatic cells specially set apart for that purpose and formingdistinct sexual organs, the ovaries and spcrniarics or their equivalents.Within these organs the germ-cells are carried, protected, and nour-ished ; and here they undergo various differentiations to preparethem for their future functions. In the earlier stages of embryological development the progenitorsof the germ-cells are exactly alike in the two sexes and are indistin- 124 ^^^ GERM-C

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