120 How Animals Changed 



heart when perfused with various solutions continues to beat' 

 through a wide range of molecular concentrations, — pH 5.5 to 9.0 

 (Lindeman, 1928). In Siam, Alexander (1932) studied a fresh- 

 water crab, Paratelphusa sinense Milne-Edwards, which survived 

 immersion in sea water (pH 3.0 to 10.0) for four hours. 



Perhaps the most primitive function of bloods in animals is that 

 of furnishing bodily tissues a solution containing the salts necessary 

 to keep cells in a physiologically balanced condition. Other primi- 

 tive functions are the carrying of nourishment and materials needed 

 for metabolic processes, as well as the wastes resulting therefrom. 

 The transportation of hormones, antibodies, leucocytes, and other 

 protective substances is also done by circulating body fluids. Many 

 bloods produce clots which effectively plug up holes produced in 

 the bodies of animals by injuries. 



As animals progress from ocean to land, their bloods are on the 

 whole less saline (Pearse, 1931, 1932b; Rogers, 1927, p. 148) and 

 more stable (Fig. 18) . Salts, which in primitive animals are like 

 those in the sea, become specific in quantity and function. They 

 keep internal media which bathe living cells constant by acting as 

 buffers and preventing acidity through combinations with the prod- 

 ucts of metabolism. More lactic acid is secreted in the active mus- 

 cles of land vertebrates than in those of aquatic anin^ls (Ritchie, 

 1927). Alkali reserves which combine with carbon dioxide or other 

 substances become subject to control by internal mechanisms and 

 are increased when such changes as decrease in oxygen or increase 

 in carbon dioxide occur in the environment (Powers SC Logan, 

 1925) . As blood functions increase and become more specific, 

 blood cells become specialized as phagocytes, antibody producers, 

 oxygen carriers, etc. Blood pigments, which perhaps first occurred 

 as inert waste products, came to serve important functions as oxy- 

 gen carriers. They may be present in the plasma or confined to 

 particular cells or corpuscles. Haemoglobin occurs in vertebrates in 

 corpuscles, except in the lancelets in which it is plasmic. It is also 



