. Zoology : for students and general readers . Zoology. ZOOLOGY. still firmer intercellular substance ; and when the intercel- lular substance becomes combined with salts of lime form- ing bone, we have hony tissue. The blood-corpuscles origmate from the mesoderm as independent cells floating in the circulating fluid, the blood- cells being formed contemporaneously with the walls of the vessels enclosing the blood. In the invertebrates the blood- cells are either strikingly like the Ammba in appearance, or â mil im ^^® oya\, but still capable of feiil^^l^^i^^l^^ changing their form. Thus bloo
. Zoology : for students and general readers . Zoology. ZOOLOGY. still firmer intercellular substance ; and when the intercel- lular substance becomes combined with salts of lime form- ing bone, we have hony tissue. The blood-corpuscles origmate from the mesoderm as independent cells floating in the circulating fluid, the blood- cells being formed contemporaneously with the walls of the vessels enclosing the blood. In the invertebrates the blood- cells are either strikingly like the Ammba in appearance, or â mil im ^^® oya\, but still capable of feiil^^l^^i^^l^^ changing their form. Thus blood- 'â¢^'*â¢"'-^â¢'^^^^^^*â¢' corpuscles arise like other tissues. Fig. 5 -strmied miiKciiiar flhriiia Qxceijt that the blood-cells are of a water beetle.âAfter Minot. i free. ifuscular tissue is also composed of cells, which are at first nucleated and afterward lose their nuclei. From being at first oval, the cells finally become elongated and unite together to form the fibrillae ; these unite into bundles forming muscular fibres, which in the vertebrates unite to form muscles. Muscular fibrillse may be simple or striated (Fig. 5). The contractility of muscles is due to the con- tractility of the protoplasm originating in the cells forming the filjrillse. Nervous tissue is made up of nerve-cells and fibres pro- ceeding from tliem ; the for- mer constituting the centres of nervous force, and usually massed together, forming a gcmglion or nerve-centre from which nerve-fibres pass to the periphery and extremities of °"â¢* ("^ the body, and serve as conductors of nerve-force (Fig. 6). Organs and their Functions.âHaving considered the difiierent kinds of cells and the tissues they form, we may now consider the origin of organs and their functions. Tho Protamoeba may be considered as an organless being. In Avmha (Fig. 11) we first meet with a specialized portion of the body, set apart for the performance of a special nnglion in the clam, wi
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
