RESPIRATION 87 



Manwell (1959) however suggests that the method of L. terrestris 

 exchanging gases through a boundary of cuticle, epidermis and 

 hypodermis is relatively inefficient, and that this is compensated by 

 the properties of the haemoglobin in the blood system (see later). 



Rate of Respiration 



As the exchange of gases takes place across the body wall it is to 

 be expected that the respiratory rate will be affected by the size of 

 the animal, and thus by the surface area. Other parameters such as 

 temperature will also affect the respiratory rate (Kriiger, 1952, on 

 E. foetida). 



L. terrestris, weighing between 2-5 and 5 g, respires at an average 

 rate of 45-2 mm^ 02/g/hr for the first hour at normal oxygen ten- 

 sions, this rate gradually dropping to 38-7 mm*^ 02/g/hr during a 

 second hour at a temperature of 10 °C (Johnson, 1942). Values of a 

 similar order, ranging between 25 and 105 mm^ 02/g/hr in air and 

 immersed in water were obtained by Raffy. At a temperature of 

 16-17 °C an individual weighing 1-47 g had a respiratory rate of 

 70 mm^ 02/g/hr, while another worm of 5-43 g respired at a 

 rate of 31 mm^ O2 g/hr; thus the larger and heavier the animal, and 

 consequently the smaller the surface area : volume ratio the lower the 

 oxygen uptake per gramme of body tissue (Raffy, 1930). 



When earthworms are submerged in water the respiratory rate 

 depends directly on the partial pressure of the oxygen dissolved 

 in the water. Table 11 shows that when the partial pressure of 

 oxygen in water drops so does the oxygen uptake rate of the 

 earthworm, and when the partial pressure rises so does oxygen 

 consumption (Raffy, 1930). 



The rate of oxygen consumption is also greatly affected by the 

 ambient temperature, a parameter likely to be of more importance 

 to an earthworm in nature than the partial pressure of oxygen in 

 water. Pomerat and Zarrow (1936) observed a variation between 

 25 and 250 mm^ per individual per 30 minutes in a temperature 

 range from 9-27 °C using the Warburg method to detect respiratory 

 exchange. They found no difference existed in the level of respira- 

 tion between normal, decerebrate and animals with no sub- 

 oesophageal ganglion. 



The problems of acclimatization which have received much atten- 

 tion recently in many groups have been studied in the species 



G 



