. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. MULTICELLULAR ANIMALS 73 muscles increases the rapidity of ventilation of the lungs. The in- creased rate of breathing continues after exercise, until the chemistry of the blood returns to normal. Many other events may stimulate the respiratory centre of the brain, for example, fright, injury, and shock; it is also under voluntary control. Food and Oxygen Transport Systems. The distribution of nutritive materials from the digestive system and of oxygen from the respiratory system, and the col
. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. MULTICELLULAR ANIMALS 73 muscles increases the rapidity of ventilation of the lungs. The in- creased rate of breathing continues after exercise, until the chemistry of the blood returns to normal. Many other events may stimulate the respiratory centre of the brain, for example, fright, injury, and shock; it is also under voluntary control. Food and Oxygen Transport Systems. The distribution of nutritive materials from the digestive system and of oxygen from the respiratory system, and the collecting of carbon dioxide and of nitrogenous and other wastes for expulsion are effected by orderly currents of liquids within the tissues. The complex system of trans- DORSAL BLOOD VESSEL DIGESTIVE TRACT. SUBNEURAL BLOOD VESSEL EXTRA-OESOPHAGEAL VENTRAL BLOOD VESSEL BLOOD VESSEL Fig. 116.—Diajjram of the circulatory system of the anterior region of an earthworm. (Partly after Stephenson: Oligochaeta. Oxford University Press.) portation that constitutes the human circulatory system appears to be the summation of various processes which take place in more simple forms. The direct respiration and excretion in Protozoa and in the simple diploblastic animals renders a circulatory medium unnecessary; the surrounding water serves that purpose. In triplo- biastic animals with deep tissues, watery circulatory liquids serve. In the flatworms, Platyhelminthes, and in the Nemathelminthes the circulatory liquid consists of a watery coelomic fluid that does not appear to be exceptionally highly developed for carrying oxygen. In most Mollusca, for example, the common oyster, and in Arthro- poda, the circulatory liquid is in part confined in tubes and contains a green compound, , containing copper, which by reac-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrat
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