. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 24 Comparative Animal Physiology Limited Osmoregulation: Invaders of Brackish Water. Eriphia spiniformis and Pachygrapsus mannorahis, --- Cancer pagitriis (Platycarcinus, Fig. 13 curve E), -^â¢^' and Cancer magister, Hemigrapsus nudus (Fig. 13, curve D), and Hemigrapsus oregonensis (Fig. 13, curve B) '-- show a slight ability to remain hypertonic in dilute sea water (Fig. 13, curves B and D; Fig. 14, curve E). These crabs are isotonic or nearly so in sea water and in higher concen- trations, and hypertonic but n
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 24 Comparative Animal Physiology Limited Osmoregulation: Invaders of Brackish Water. Eriphia spiniformis and Pachygrapsus mannorahis, --- Cancer pagitriis (Platycarcinus, Fig. 13 curve E), -^â¢^' and Cancer magister, Hemigrapsus nudus (Fig. 13, curve D), and Hemigrapsus oregonensis (Fig. 13, curve B) '-- show a slight ability to remain hypertonic in dilute sea water (Fig. 13, curves B and D; Fig. 14, curve E). These crabs are isotonic or nearly so in sea water and in higher concen- trations, and hypertonic but not constant in blood concentration in increasing- ly dilute media. They are rock crabs occurring along the shore, sometimes in tidal pools. One important factor in their regulation is low permeability to water and salts. Figure 9 shows that in 66 per cent sea water Cancer swells â Fig. 13. Blood concentrations (Ai) as a function of external concentrations (Ao) in several Crustacea which are labile in hypertonic media and show some regulation in hypotonic media. A Pachygrapsus crassipes; ⢠Heniigrapsiis oregonensis; â Rhithro- panopeus harrisii; Q Hemigrapstis nudus. Data from Jones.^"" less than does Maja in 75 per cent sea water, but that Cancer recovers more slowly in volume. Hence Cancer is less permeable to both water and salt. In a hypertonic medium ( per cent salinity) the blood of Eriphia reached a concentration equal to that of the medium only after 72 hours, whereas Maja reached the same concentration as the medium in 12 hours (Fig. 11). --- A useful method for investigating salt permeability is to place crabs in sea water containing small amounts of iodine and to measure the amount taken up. When Cancer was bathed in sea water containing per cent iodine, the crab took up to mg. iodine / cc. of blood after 7 to 8 hours. '^^ When the intestine was plugged the uptake was the same. When a tube containing per cent sodium iodi
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