90 THE PHYSIOLOGY OF EARTHWORMS 



surface of the body. This is possibly due to dilation of the skin 

 capillaries, and a reverse effect is obtained upon the use of acetyl- 

 choline, the respiratory rate being decreased, probably due to 

 constriction of the capillaries. These results may be spurious as 

 very concentrated adrenaline and acetylcholine solutions were used 

 in order to overcome the barrier provided by the mucus secretion 

 of the body wall. The mucus does not contain any cholinesterase 

 activity (Mendes and Nanato, 1957). It would be interesting to 

 know if respiratory rates are increased when adrenaline is injected 

 into the blood system. The pseudohearts and general circulation of 

 L. terrestns function more rapidly when adrenaline (10-^ g/1.) is 

 injected (Prosser and Zimmerman, 1943), and this may be reflected 

 by the oxygen consumption of the animal. 



Patterns of Gaseous Excha?ige 



That the respiration of animals, and indeed plants as well, is not 

 a constant throughout the day, or throughout the seasons of the 

 year, is now well known and has recently been reviewed by Harker 

 (1958). Diurnal, lunar, monthly and annual cyclic changes of 

 respiratory rates are known to be widespread. 



The earthworm also shows a fluctuating respiratory rhythm. 

 Records continuous for up to 2 months are available of the course 

 of respiration of L. terrestns. Experiments were carried out in 

 unvarying conditions of temperature, humidity and low illumina- 

 tion using the buoyant respirometer described by Brown (1954). 

 Analysis of kymograph recordings made in this way led Ralph 

 (1957) to conclude that earthworms show a diurnal rhythm in 

 oxygen consumption which showed maximal rates at about 

 6 a.m. and again at approximately 7 p.m. Minimal rates 

 occurred at about 10 p.m. Further statistical manipulation of the 

 results was claimed to show that lunar day (24-8 hr) and lunar 

 (29-5 days) cycles were also part of the make up of respiratory 

 rhythms in L. terrestris (Fig. 27). 



The method used in this study has been severely criticized by 

 Cole (1957) and further investigations with a different method 

 might be advisable. This is particularly pertinent in view of the 

 fact that Ralph (1957) found that periods of maximum locomotor 

 activity are associated with low oxygen consumption rates (Fig. 27) 

 and suggested that earthworms accumulate oxygen debts at such 



