2 THE PHYSIOLOGY OF EARTHWORMS 



earthworms, however, was performed before the methods men- 

 tioned above were in use. It is none the less interesting, as it is hoped 

 to show in the pages that follow. 



Undoubtedly the major chemical component of the oligochaete 

 body, as that of any animal body, is water. The amount of water 

 present in the earthworm has been variously estimated at 81-3% 

 (Durchon and Lafon, 1951), 84-1% (Schmidt, 1927), 84-8% 

 (Roots, 1956) and 88-0% (Jackson, 1926) of the entire body weight. 

 This water is distributed in the coelom, blood vascular system and 

 the tissues themselves. In both terrestrial and fresh-water oligo- 

 chaetes the proportion of body water is always subject to change, 

 often rapid, due in the main to desiccation in the land forms, 

 flooding under osmotic stress in the fresh-water types, and the 

 secretion of mucus by both classes. 



Earthworms of the species Lumhricus terrestris and Allolohophora 

 caliginosa show regional differences in the water content of the 

 integument, the anterior portion containing more than the posterior 

 extremity. The capacity of the body wall to take up water also 

 varies from place to place, and a minimum supply of calcium ions, 

 an important factor in membrane permeability, is necessary to 

 prevent flooding of the interior with water which passes rapidly 

 through the body wall from the external environment. Hydro- 

 phobic substances such as lipids also play a part in maintaining 

 a water barrier in the integument, for if they are removed by 

 alcohol treatment water uptake, particularly in the anterior regions, 

 is very rapid (Kopenhaver, 1937). 



Variations in integumentary water contents have also been 

 described for two Indian species, Pheretima posthiima and Lampito 

 (Megascolex) maiiritn, in both of which the amount of water, 

 estimated in pre-clitellar, post-clitellar and rectal fragments, 

 increases from the anterior to posterior regions. At the same time 

 it is found that the absolute quantity of water present in these 

 Indian earthworms is lower than that reported for temperate 

 species. This may indicate that the drier soils of the tropics in- 

 fluence the water content of the integument, although no informa- 

 tion is given as to what happens to the water content when rainy 

 monsoon conditions prevail (Tandan, 1951). It has been shown 

 that in temperate countries earthworms obtained fresh from the 

 soil are rarely fully hydrated and indeed may absorb up to 15% 



