72 



THE PHYSIOLOGY OF EARTHWORMS 



be lost without causing death (Roots, 1956, Schmidt, 1927). 

 As dehydration becomes more pronounced a series of behavioural 

 changes occurs; at first there is a prostomial reaction, when it is 

 noted that the ability of a substrate to induce dehydration of the 

 body calls forth a ''dehydration tropism". Parker and Parshley 

 (1911) found that the response was localized on the prostomium, 

 the removal of which stopped the reaction, the response being 

 shown again when the prostomium regenerated. This tropism is 

 followed by a period of rolling, and then coelomic fluid is expelled 

 from the dorsal pores in an endeavour to moisten the body surface, 

 but if the desiccation is unrelieved this is followed by rigor, 



Losses through 



dorsal pores (Wolf 1938) 



Losses from 

 gut 



(Moluf 1936 

 Bohl J947) 



Losses through 

 skin surface 



(Jackson 1926 

 Roots 1951) 



Chloride 



uptake through 



skin 



(Van Brink and 



Rietsema 1949 



Maluf 1936) 



Losses fronn 

 nephridia 

 ©ah! 1947 

 Ramsay 1949) 



Intake through 

 skin 



(Kopenhaver 1937 

 Wolf 1938) 



Fig, 22. Diagram summarizing routes of water loss or gain in the 



earthworm. 



anabiosis and finally death (Wolf, 1938). Providing that irrever- 

 sible internal changes have not occurred animals can be revived by 

 submersion after very large water losses. 



Water is lost readily through the skin, and it can be gained by the 

 same pathway from the external environment with equal facility. 

 L. terrestris ligatured at both anterior and posterior ends prior to 

 immersion in w^ater gains weight, about 7%, and then maintains a 

 constant weight level (Maloeuf, 1940 a, b). Not only can water be 

 taken in via the body wall, so also can salts. Chloride ions disappear 

 from dilute salt solutions containing worms due, it is thought, to 

 active uptake of the ions (Maloeuf, 1940a; Van Brink and Rietsema, 

 1949). 



