Hand-book of physiology (1892) (14762759424)

Identifier: handbookofphysio00bake (find matches)

Title: Hand-book of physiology

Year: 1892 (1890s)

Authors: Baker, W. Morrant, (William Morrant), 1839-1896 Harris, Vincent Dormer Kirkes, William Senhouse, 1823-1864. Hand-book of physiology. 13th ed

Subjects: Physiology Human physiology

Publisher: London : John Murray

Contributing Library: Francis A. Countway Library of Medicine

Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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shape from mutual pressure, called the Blastoderm, is formed,and this speedily divides into two and then into three layers,chiefly from the rapid proliferation of the cells of the first singlelayer. These layers are called the Epiblast, the Mesoblast,and the Hypoblast (fig. 18). It is found in the further development of the animal that fromeach of these layers is produced a very definite part of its com-pleted body. For example, from the cells of the epiblast, arederived, among other structures, the skin and the central nervoussystem; from the mesoblast is derived the flesh or muscles of the CH. II) DIVISION OF FUNCTION. 23 body, and from the hypoblast, the epithelium of the alimentarycanal and some of the chief glands, and so on. It is obvious that the tissues and organs so derived exhibit ina varying degree the primary properties of protoplasm. Themuscles, for example, derived from certain cells of the mesoblastare particularly contractile and respond to stimuli readily, whilst the

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Fig. 18.—Transverse section through erubryo chick (26 hours), a, epiblast; i, mesoblast;c, hypoblast; d, central portion of mesoblast, which is here fused with epiblast;e, primitive groove ; /, dorsal ridge. (Klein.) cells of the liver, although possibly contractile to a certain extent,have to do chiefly with the processes of nutrition. Thus, in development, we see that as the cells of the embryoincrease in number it speedily becomes necessary for the organism todepute to different groups of cells, or to their equivalents (i.e., to thetissues or organs to which they give rise), special functions, so thatthe various functions which the original cell may be supposed to dis-charge, and the various properties it may be supposed to possess,become divided up among various groups of resulting cells. Thework of each group is specialised. As a result of this division oflabour, as it may be called, these functions and properties are, asmight be expected, developed and. made more perfect, whil

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1892

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