RESPIRATION 



189 



creased C0 2 , rise in acidity and elevation of temperature raise unloading 

 tensions (Fig. 4.23). It has been computed that the effect of tissue levels of 

 C0 2 on the dissociation of oxyhaemocyanin would account for about a 

 third of the oxygen exchange in the squid (Loligo). Cephalopods, in 

 general, are moderately to highly active animals, living in well-aerated 



20 



90 



WO 



30 40 50 60 70 80 



Oxygen Tension (mm Hg) 



Fig. 4.22. Oxygen Dissociation Curves of Haemocyanins 

 of Several Arthropods and Molluscs 



Limulus polyphemus, pH 7-35, 25°C; Busycon canaliculatum, pH 8-35, 25 C C; Homarus 

 americanus, pH 7-72, 25 C C; Loligo vulgaris, 5-3 mm CO,, 20°C (from various sources). 



waters, and their haemocyanins function to the full in oxygen transport 

 under such conditions (130, 169). 



The oxygen capacities of other haemocyanin-containing bloods are 

 rather low, ranging from 1 to 3 vols% in gastropods, decapod crustaceans 

 and Limulus. The dissociation curves are similar in shape to those of 

 haemoglobins and are very diverse. On warming there is a marked increase 

 in loading and unloading tensions, but the effects of acidity and CO a 



