. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 86 Comparative Animal Physiology time when their ancestors' blood became separated within a closed circulation, whereas the fluids of animals like Aurelia and Limulus have changed with the ocean, changes in calcium and potassium occurring^ faster than changes in sodium, magnesium, and especially sulfate. Changes in the environment and in the organisms were thought to be very slow. Macallum suggested that the circulatory system of ancestors of the lobster was cut off from the sea very early, and that possibly the
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 86 Comparative Animal Physiology time when their ancestors' blood became separated within a closed circulation, whereas the fluids of animals like Aurelia and Limulus have changed with the ocean, changes in calcium and potassium occurring^ faster than changes in sodium, magnesium, and especially sulfate. Changes in the environment and in the organisms were thought to be very slow. Macallum suggested that the circulatory system of ancestors of the lobster was cut off from the sea very early, and that possibly the modern lobster came from fresh-water ancestry. Un- fortunately for the theory, the circulatory system of the lobster is open, like that of Limulus. Macallum's general theory was well supported, with respect to the vertebrates, by geological evidence regarding the composition of the ocean at different 8 10 c 12 14 16 18 20 22 24 26 Iq (MG/ML) Fig. 23. Concentration of chloride in blood (Cli) in as a function of chloride in the medium (CL), in Mesidotea and Astacus. From ;' "^ Fredericq ''^ also emphasized the rapid movement of water and slow changes in ions in the blood of various marine invertebrates on transfer to dilute media. Tests of Macallum's hypothesis and of the limitations imposed by salt balance on animal distribution have been made by placing aquatic animals in sea water of different tonicities, or in solutions containing ions in proportions differing from those in the customary media, then measuring the changes in composition of the animals' blood. The effects on ionic composition of transfer to different concentrations of sea water are shown for several crustaceans in Table 12 and Figures 23-25. When fresh-water crustaceans such as Astacus or Telphusa or a fresh-water Eriocheir is transferred to various dilutions of sea water, numerous changes occur. The water content of blood and of muscle may diminish slightly; the. Please note t
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