WATER RELATIONS 71 



weight and accompanying volume changes serve to show that 

 under normal field conditions the earthworm maintains a water 

 equihbrium with fair efficiency. The locomotory and burrowing 

 efficiency of annelids depends to a large extent upon the hydrostatic 

 skeleton of the coelomic ffuid and loss of water in particular may 

 interfere with normal behaviour. Water losses and gains of the 

 magnitude mentioned above do not affect the normal locomotion 

 and activity of the animal, a loss of some 18% being tolerated 

 before overt changes in behaviour patterns are observed (Wolf, 

 1940). Slight diurnal alterations in body weight amounting to an 

 average of 2-3% of the basal weight occur which have little 

 significance, but if earthworms are kept in distilled water for up to 

 16 days there is, after an initial gain, a gradual loss of weight which 

 may be due to leaching of salts from the internal fluids (Wolf, 1940). 



Roots (1956) found that many species of earthworm are able to 

 live in waterlogged soil which has standing water above it. Survival 

 of L. terrestris, A. chlorotica and A. longa among others was for 

 31-50 weeks in such conditions, and the animals remain alive for 

 72-137 days without food. Many individuals in such conditions 

 remain partly stretched above the surface of the soil in the water 

 layer. Burrows made in waterlogged soil are not irrigated as are 

 those of burrowing polychaetes. Roots suggests that the long 

 survival of earthworms under water depends not upon the ability 

 to control the water circulation of the body, but upon the ability to 

 withstand prolonged starvation. Earthworms will leave water- 

 logged soil in preference for a drier site if possible. 



The respiration of earthworms takes place through the body 

 surface, without the aid of special anatomical structures. It is 

 essential for gaseous exchange to take place that a thin film of 

 moisture be maintained at the interface between the air and the skin, 

 in order that oxygen may go into solution before passing across the 

 boundary of the skin and into the blood system. Obviously if the 

 animals live in a moisture-saturated atmosphere it is a comparatively 

 simple task to maintain a layer of water over the skin since 

 evaporation will be at a minimum. Soil conditions are rarely stable 

 with regard to moisture content, however, and if they become dry 

 then earthworms lose moisture from the body. An attempt is 

 made to keep the surface moist and if water is continually lost the 

 animal loses weight. Up to about 75% of the total body water may 



