238 



INVERTEBRATE PHYSIOLOGY 



and sulphate are much below those of sea water, and sodium, potassium, 

 calcium, and chloride higher. 



TABLE 4. IONIC COMPOSITION OF THE BODY FLUIDS OF SOME 

 FRESHWATER INVERTEBRATES AND PARASITES 



Anodonta Sialis Gastrophilus Ascaris 



cygnea* lutaria'[ intestinalist lumbricoides^ 



(lamellibranch) (neuropteran) (dipteran) (nematode) 



mE/kg.HaO mE/Iiter mE/kg.H^O mE/liter 



Na 15.6 109 206 " 129 



K 0.49 5 13 25 



Ca 16.8 15 7 12 



Mg 0.38 38- 38 10 



CI 11.7 31 17 53 



SO4 1.5 .... 6 



HCO3 13.6 15 17 



HPO4+H2PO4 0.4 .... 40 26 



Other anions .... 75 



Total cations 33.3 167 264 176 



Total anions 27.2 46 155 79 



Total ionic concentration 



in mg. ions 50.9 187 ca 347 234 



A °C of body fluid 0.078 ca 0.63 0.872 0.655 



A °C of environment ca 0.02 ca 0.01 ? 0.8 0.869 



* Potts (19S4a). 

 tShaw (1955a). 

 tLevenbook (1950). 

 §Hobsonetal. (1952). 



Table 4 gives some indication of the range in composition of body fluids 

 in fresh-water and parasitic animals, and the relatively incomplete data 

 available for the anions in three of the animals. In Anodonta the concentra- 

 tion of calcium exceeds that of sodium, but about 5 mE are believed to be 

 present in some nondififusible, nonionized form. The high calcium value is 

 related to the fact that in this shelled mollusc the blood is saturated in re- 

 spect to calcium carbonate (Potts, 1954a). Sialis larvae like other insects 

 maintain a fairly high osmotic concentration, but the inorganic ions account 

 for little more than half. Presumably free amino acids make up the deficit, 

 and Shaw (1955a) suggests that dicarboxylic amino acids may make up 

 the anion deficit. 



Similar discrepancies occur in the horse-bot larvae Gastrophilus and 

 Ascaris from the pig. In the former organic acids and unidentified phos- 

 phorus compounds form a large fraction of the anions, and free amino 

 acids come to about 73 mM/kg. water, or about 15% of the total osmotic 

 concentration. Although Ascaris body fluid is markedly hypo-osmotic to 

 the contents of the small intestine of the pig, the electrolyte composition 

 of the two fluids is very similar (Hobson et al., 1952). 



