88 Comparative Animal Physiology 



Blood chloride appears to be more labile than tissue chloride in crustaceans. 

 When gammarids (fresh-water, brackish, and marine species) were trans- 

 ferred to media of different tonicities, the blood chloride changed more than 

 the muscle chloride did (Fig. 25). Eriocheir, which is marine-like in excreting 

 a small volume of near-isotonic urine, has a blood-to-tissue Cl~ ratio of 280:43, 

 whereas in Astacus, which excretes copious dilute urine, the blood-to-tissue 

 CI" ratio is 189:378. The ions of Eriocheir and Astacus bloods change dis- 

 proportionately in different media. ^^ In Mytilus, on the other hand, the 

 blood chloride changes in proportion to the sea water chloride, but changes in 

 muscle chloride are greater. ''** Changes in blood and tissue chloride occur 

 rapidly in Mytilus, and the animals die if their chloride content is severely 

 depleted. ^^ 



B lood 



200- 



. / ^ Tissue CI 



100 200 300 400 500 600 



S.W. EQUIVALENT mM No CI 



Fig. 25. Blood osmotic pressure (O.P.), blood chloride (CI) as mM NaCl/1., and 

 tissue chloride (CI) as mM NaCl/kg. wet wt. in Gammarus dueheni (brackish), G. 

 ohtusatus (marine), and G. pulex (fresh-water) in dilutions of sea water corresponding 

 to the concentrations of NaCl given on the abscissa. From Beadle and Cragg.*" 



When mosquito larvae (Aedes detritus) are in different dilutions of sea 

 water, both total osmotic concentration and chloride concentration are well 

 regulated, but they show progressive changes with external concentration, os- 

 motic concentration and chloride content changing disproportionately. Larvae 

 of Aedes aegypti regulate CI" well in dilute but not in hvpertonic media 

 (Fig. 26). 



The effects of disproportionate changes in particular elements also indicate 

 selective ionic regulation. Those animals with some ions present in nearly 

 the same concentration as in sea water change their concentration of these ions 

 readily. Sea anemones ^^ in dilute sea water increase their water and decrease 

 their calcium concentration, whereas in a mixture of sea water and isotonic 



