Excerpt from The Biology of the Protozoa While the single protozoon is to be compared structurally with a single isolated unit tissue cell of a metazoon as a bit of protoplasm differentiated into cell body, or cytoplasm, and nucleus, it is a very different unit physiologically. In its Vital activities it should be compared, not with the unit tissue cell, but with the entire organism of which the tissue cell is a part. All animal organisms perform the same fundamental vital activities of nutrition, excretion, irri tability ...
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Excerpt from The Biology of the Protozoa While the single protozoon is to be compared structurally with a single isolated unit tissue cell of a metazoon as a bit of protoplasm differentiated into cell body, or cytoplasm, and nucleus, it is a very different unit physiologically. In its Vital activities it should be compared, not with the unit tissue cell, but with the entire organism of which the tissue cell is a part. All animal organisms perform the same fundamental vital activities of nutrition, excretion, irri tability with movement and reproduction, which are fundamental attributes of living animal protoplasm. In the higher types of Metazoa these primary activities are performed by complex organ systems, nutrition for example, involving not only the digestive system but the muscular, nervous, circulatory and respiratory systems as well. Each organ has its particular part to play in the economy of the whole and each cell is differentiated for the purpose of its specialized function. T issue cells, therefore, are physiologic ally unbalanced cells since they are preeminently specialized for secretion, or contraction, or irritability, etc. Division of labor in a physiological sense here reaches its highest expression. In the lower Metazoa the organ systems are less highly special ized; fewer organs are present to perform the same fundamental Vital activities and the tissue cells have relatively more kinds of work to do for the organism as a whole. Thus the supporting and covering cells of a coelenterate combine the functions of respiration, irritability, muscular contraction, excretion and circulation with the primary functions of an epithelium. Each of them is more nearly balanced physiologically than a single cell of the higher types, but it still needs the activities of other cells, and the organism is again the sum-total of all its cellular parts. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at ... This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.
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