EXCRETION AND WATER BALANCE 47 



cells normally accumulate pigmented granules and it is reasonable 

 to assume that they correspond in part with the chloragogenous 

 cells of other annelids. Cuenot further showed that when indigo 

 sulphate is introduced to the coelomic cavities it is taken up by the 

 vaso-fibrous tissue of Hirudo (p. 21) and by the large pigment cells 

 in the connective tissue of rhynchobdellids. Tilloy (1937) carried 

 the investigation further and concluded that in general the 

 botryoidal tissue of gnathobdellids and coelomic epithelial cells 

 of rhynchobdelUds take up particles of diameter greater than 

 10 A while the vaso-fibrous tissue of Hirudo and the pigment cells 

 of rhynchobdelUds take up those of diameter less than 10 A. 



The only histochemical investigation of these excretory tissues 

 by modern methods is that of Bradbury (1957, 1959). He was 

 concerned primarily with the metabolism of iron, which is an 

 important constituent of the diet of blood-sucking leeches. The 

 haem probably breaks down to yield first a porphyrin and then 

 linear tetra-pyrrole compounds similar to vertebrate bile pigments. 

 These substances have been identified in the vaso-fibrous tissue 

 oi Hirudo and in the large pigment cells of Glossiphonia complanata. 

 Bradbury thinks that these are the sites of haem metabolism. In 

 the case of the pigment cells of Glossiphonia it appears that they 

 are derived from adipose cells which are such a conspicuous 

 feature of the parenchyma of this leech. Tetra-pyrroles accumulate 

 in the adipose cells until there comes a point when the cytoplasm 

 degenerates leaving an envelope containing a mass of pigmented 

 spheres. Previously it has been thought that these pigment cells 

 were derived from coelomic epithelial cells or from amoebocytes 

 but it now appears more likely that they are in fact derived from 

 adipose cells which function as kidneys of accumulation. 



Bradbury failed to identify the pigment present in the botryoidal 

 tissue of Hirudo, but established that it is soluble in weak sodium 

 hydroxide and in glacial acetic acid. He found that iron was present 

 in the botryoidal tissue but not in the vaso-fibrous tissue. It there- 

 fore appears that during the metabolism of haem the pyrrholes 

 pass to the vaso-fibrous tissue while the iron is stored in the 

 botryoidal tissue. An investigation of the fate of the products of 

 protein metabolism in leeches along the lines of that of Semal-van 

 Gansen in earthworms, is much needed. Robin et al. (1957) 

 identified a new guanidine derivative in the muscles of Hirudo. 



