Inorganic Ions 



81 



Departure from unity in this ratio and maintenance of a given ionic composi- 

 tion when the external medium is changed reflect ionic regulation. The 

 amount of magnesium and sulfate in the marine environment is much greater 

 relative to other ions than is the amount in the environment of freshwater 

 animals. Animals which adjust osmotically to the medium may regulate ion- 

 icallv. 



TABLE 10. AVERAGE VALUES OF BLOOD OR OTHER BODY FLUID 



pH OF A VARIETY OF ANIMALS, SELECTED FROM THE 



EXTENSIVE LITERATURE 



Table 1 1 shows that in echinoderms there is practically no ionic regulation 

 in the inorganic composition of the coelomic fluid except for a slightly higher 

 potassium concentration. The ambulacral fluid is continuous with sea water, 

 except in holothurians, and the coelomic fluid in all echinoderm classes which 

 have been examined is more similar to sea water than that in any other 

 phylum. Despite the similarity of echinoderm body fluid to sea water, the 



