26 OLIGOCHAETA 



cells upon the nervous system. The layer of peritoneum covering the alimentary 

 canal is greatly modified, particularly upon the intestinal region. To this layer the 

 name of ' Chloragogen-cells ' was applied by CLAPAREDE. The layer was at one time 

 thought to be a digestive gland; and the fact that the cells end in a finish thread 

 which is closely applied to the wall of the intestine favoured the supposition. It 

 was pointed out however by CLAPAREDE that these cells are not so much connected 

 with the intestine as with the blood-vessels upon its surface. According to KUKENTHAL 

 their function is that of extracting waste substances from the blood and setting them 

 free into the body-cavity whence they are removed by the nephridia. These chloragogen- 

 cells contain greenish to blackish granules, the pigmentation being more marked in 

 some species than in others. Upon the nephridia the coelomic epithelium often shows 

 a different modification ; the nephridia are of course always enveloped in a layer of 

 this tissue as are all the organs lying in the coelom (except the gonads, which are 

 peritoneum) ; but it is frequently a thin and barely discernable layer ; this is not 

 the case with the aquatic Oligochaeta ; but those worms which appear to have 

 the densest peritoneal layer round the nephridia are the Eudrilidae. The cells 

 are often loaded with round granules of various sizes ; the presence of these 

 gives the nephridia, when viewed with the naked eye, a very conspicuous and 

 white appearance. The coelomic cells which line the spermathecal pouches in the 

 Eudrilidae are also very large ; they are pear-shaped and are often apparently in 

 a condition of rapid proliferation. It is quite otherwise with the cells lining the sperm- 

 sacs and the ovisacs ; in these sacs the peritoneal layer is but little conspicuous. 

 The peritoneum, if it be really so, which lines the large spermathecal sac of 

 Polytoreutus, has quite the appearance of a columnar epithelium. There is a further 

 peculiar modification of the coelomic epithelium enveloping the remarkable calciferous 

 glands of many Eudrilidae for which see the description of those glands. 



The coelomic cavity of the Oligochaeta also contains free corpuscles. In the 

 higher Oligochaeta these are apparently of two kinds ; there are small amoeboid 

 corpuscles and large spherical corpuscles loaded with granules ; in addition to the 

 corpuscles there is also a certain amount of fluid which is coagulated by alcohol. The 

 two kinds of corpuscles referred to are probably merely stages in growth ; when 

 the cell becomes loaded with excretory (?) products it naturally loses its activity 

 of movement and assumes the spherical form referred to. Very remarkable are the 

 elliptical corpuscles of the Enchytraeidae ; these have a fixed outline ; sometimes 

 there are round as well as oval corpuscles in the same species. 



In the lower Oligochaeta the corpuscles are often extremely abundant; this is 

 particularly the case with the Enchytraeidae and the Naidomorpha ; in the latter 



