244 INVERTEBRATE PHYSIOLOGY 



Summary 



Characteristic patterns of ionic regulation are found in the marine in- 

 vertebrates, although most of these animals show no osmotic regulation. 

 These patterns vary from slight regulation in the more simply organized 

 groups like echinoderms, polychaetes, and lamellibranchs to pronounced 

 regulation in the more highly organized Crustacea and Cephalopoda. In 

 the two latter classes, selective excretion of ions in the excretory fluids 

 and controlled uptake of ions by the more permeable surfaces are essential 

 features in their ionic regulation. A correlation between level of mag- 

 nesium in the blood plasma and the activity of the animals is evident in 

 the decapod crustaceans, the more active ones having low values of mag- 

 nesium. 



Calculations by Potts (1954c) of the osmotic work done at the body 

 surface and excretory organs of brackish- and fresh-water animals show 

 that in Anodonta and Eriocheir it amounts to less than 2% of the total 

 metabolic energy. 



In aquatic insect larvae the Malpighian tubules can regulate the sodium 

 and potassium concentrations in the blood. 



The osmotic concentration of the blood of insect larvae as found by 

 freezing-point measurements cannot yet be accounted for by the sum of 

 analyzed constituents, and serious discrepancies exist in the matter of 

 cation-anion balance. However, fairly satisfactory agreement is found in 

 these respects between crustacean nerve and bathing fluid, and between 

 crustacean muscle and plasma. 



In two out of three crustaceans the intracellular potassium concentra- 

 tions in muscle and extracellular potassium are not in Donnan equilibrium 

 with extracellular and intracellular chloride. 



REFERENCES 



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