516 F. W. GAMBLE AND J. H. ASHWOBTH. 



of small spherical yellow granules whicli are not stained by 

 haematoxylin. In another specimen of the same species the 

 distal fourth of the cell is almost hyaline, containing only a 

 small amount of granular protoplasm ; and the concretions, 

 which are in this example all yellow, are situated in the 

 middle part of the cell only. In nephridia from full-sized 

 specimens the cells invariably present the appearances 

 described above, the distal portion of the cell being very 

 constantly free from granules. Granules are discharged 

 from the cells into the cavity of the nephridium, as we have 

 found rather large collections of yellow excretory granules 

 in the lumen of the organ. We believe each cell bears a 

 long cilium, but it is very difficult to distinguish between 

 cilia, the very thin walls of the distal portion of adjacent 

 cells, and also the fibrils of the coagulum in the nephridial 

 cavity ; but we have seen in some preparations cilia similar to 

 those drawn by Benham in A. marina (1891, pi. xxv, fig. 

 41). In this case, as in A. ecaudata, each cell bears a 

 single moderately long flagellum (about 5ju in length) on its 

 clear distal end. 



Both the funnel and the secreting portion of the nephri- 

 dium are covered by a thin laj^er of coelomic epithelium. In 

 the middle region of the secretory portion of the organ there 

 is a very thin, almost structureless layer, apparently of the 

 nature of connective tissue, between the secretory cells and 

 the ccelomic epithelium, while in the walls of the posterior 

 portion, i. e. the vesicle, there is a thin layer of muscle-fibres 

 in a corresponding position between the two cell layers. In 

 young specimens the cells of the vesicle contain fewer granules 

 than those of the secreting portion of the nephridium, but in 

 old specimens there is little difference in this respect between 

 the cells of the two regions. 



Blood-vessels of the Nephridia. — All the nephridia 

 of the various species of Arenicola (except the first and 

 second of A. Grubii and A. ecaudata) are supplied with 

 blood by segmentally arranged branches of the ventral vessel. 

 The first nephridia of A. Grubii and of A. ecaudata are 



