FUNCTIONS OF BLOOD 



109 



respiration and live on its oxygen store. In the case of these 

 and probably several other animals it is not possible to 

 distinguish sharply between the transport function and the 

 storage function of haemoglobin, but it can be stated generally 

 that in cases where the total oxygen capacity of the blood in an 

 invertebrate is high compared with its metabolism there is 

 reason to suspect a storage function. 



Fig. 63. 



tSOWn. 



Decrease in oxygen content in lungs of Limncea stagnalis and Planorbis 

 corneus when kept under water. (Hazelhoff.) 



A storage function of a definitely rhythmic character is 

 described by Lindroth (1938) for Nereis virens and will prob- 

 ably be discovered also in other animals. Nereis burrows in 

 sand which is practically oxygen-free. It will make respira- 

 tory movements for about 5 minutes and then keep quiet for 

 20-30 minutes during which the oxygen in the blood will be 

 used up and in addition some oxygen debt incurred which 

 provides the stimulus for the next ventilation period. During 

 the non-ventilating periods the blood is withdrawn from the 

 respiratory appendages and the whole circulation reduced. 

 The oxygen transport during this period is largely brought 

 about by diffusion, while the loading of the haemoglobin is 

 greatly assisted by circulation. 



Hcemocyanins are found in the blood of a majority of molluscs 

 and crustaceans and in some arachnomorphs including 



