FUNCTIONAL ADAPTATION 



SUBMAMMALIAN PIGMENTS 



333 



mammals. The actual amount of pigment carried and its affinity for 

 oxygen appear to be independent. 



The position is complicated by the greater prominence of anaerobic 

 metabolism in certain species. Thus Wigglesworth (3080, p. 221) 

 points out that Gastrophilus larvae are able to live under anaerobic 



TABLE IX 



Loading and Unloading Tensions of Oxygen Carriers'^ 



"According to Carter (^j(0). tfj = unloading tension, /£, = loading tension. 



conditions; yet Keilin (14.83) has shown that the hemoglobin in their 

 tracheal cells is o.xygenated if the larva comes in contact with a gas 

 phase containing oxygen and is thereafter reduced by the organism. 

 The extremely high affinity for oxygen of this pigment, of that con- 

 tained in the species of Planorbis which prefers to live in still water 

 with low oxygen pressure, or of that of the hemoglobin-containing 

 species of Chironomus (1853), may represent an attempt to make the 

 best of their environment. For further discussion of the latter species 

 see Maluf (1853, p. 175) for references. A similar argument applies 

 in the case of Ascaris (Davenport, 533). For discussions of how the 

 adaptation to low oxygen pressure is related to the lower environ- 

 mental temperature in many of these animals, the reader is referred 

 to Barcroft (139, lU) and to the work of Marcela and Seliskar (1868). 

 The relation of the partial pressure of carbon dioxide to the affinity 

 of the pigment for oxygen is discussed by Carter (410) in consideration 

 of Krogh and Leitch's data (1580) for the oxygen dissociation of 

 hemoglobin of fish. The partial pressure of the carbon dioxide in the 

 thin stationary layer of water surrounding the gills of animals living 

 in an aqueous environment is much lower than that in the alveolar 



