74 THE PHYSIOLOGY OF EARTHWORMS 



blood has a greater chemical content than the coelomic fluid. 

 Analysis of the chloride content of the body fluids reveals that only 

 about half of the osmotic pressure in L. terrestris can be accounted 

 for as chloride, the remainder possibly being made up by organic 

 substances (Ramsay, 1949a). The chloride content of the blood of 

 P. posthmna, however, is only half that of Liifnbricus, so it would 

 seem that in this species organic substances such as glucose, 

 protein and other large molecules must provide an even greater 

 proportion of the total osmotic pressure. 



The earhest work on the maintenance of constant internal 

 conditions is due to Adolph (1927) who believed that all the water 

 exchange of earthworms is carried out by two agencies. Water 

 enters through the skin, a process which goes on very easily, and is 

 removed via the intestine. The nephridia play no part at all in 

 excretion of water. This view was contested by Wolf (1940) who 

 found that the loss in weight sustained by worms when handled 

 was due mainly to expulsion of fluid from the nephridiopores, and 

 Adolph (1943) later accepted this observation. 



A possibility that both types of excretory process may occur was 

 suggested by Maloeuf (1939). He considered that water entered the 

 body across the body wall, was stored in the gut, and later removed 

 via both the nephridia and the gut. The gut was thought to be 

 particularly important in conditions which place the nephridia 

 under great stress, such as when the animal is placed in water and 

 is subjected to continual flooding by water entering by diffusion. 

 It was shown that if the gut w^as ligatured so that the contents could 

 not be removed the animal swelled as more and more water 

 diluted the coelomic fluid. Some control was exerted by the nephri- 

 dium and Maloeuf (1939) thought that the urine must be hypo- 

 tonic to the body fluids in order to remove the vast excess of water, 

 but he was not able to check his ideas by actual measurements. 

 Later Maloeuf (1940b) obtained figures for the osmotic pressure 

 of the gut contents and found it to be only slightly less than that 

 of the body fluids and thus was probably not after all involved in 

 water excretion ; the slight excess of water being used as lubrication 

 for the soil particles within the gut. 



It must be remembered that the environment of the earthworm is 

 terrestrial. Fresh- water oligochaetes, about the excretion of which 

 nothing is known, might be expected to be always pumping water 



