2 28 /• PERCY MOORE. [Vol. X. 



nephridium, extend transversely across the intestine, in contact 

 with the anterior face of the septum 4-5. The tubules of this 

 region are more or less enveloped by greatly enlarged peritoneal 

 cells, which enwrap the groups of tubules, and become more 

 or less fused with their fellows into a continuous protoplasmic 

 mass, though many stand out freely from this mass, and, in 

 the living worm, are swept backward and forward with currents 

 of the coelomic fluid produced by the heart's pulsations, etc. 

 Even in the mass of cells the boundaries are often perfectly 

 evident, and the cells may even be widely separated (Figs. 36 

 and 37). Their central protoplasm is arranged in a coarse net- 

 work, the meshes of which become smaller, and finally almost 

 indistinguishable at the periphery. The nuclei are large and 

 distinctly nucleolated (Figs. 36 and 37). 



The tubules themselves, including the terminal portions 

 quite to the point of union with the vesicle, are made up of 

 tubular cells joined end to end in a continuous chain, with a 

 continuous central lumen. This lumen exhibits slight irregu- 

 larities in diameter, and may wind more or less from side to 

 side within the substance of the cell. Where two cells are 

 joined the lumen almost invariably develops two, three, or four 

 short caeca (Fig. 35), which sometimes reach almost to the 

 surface of the cell, and may run together more or less to form 

 an irregular chamber. Midway between two of these nodal 

 points the nucleus may always be seen lying close to the 

 lumen. At the point where the tubule leaves the body cavity 

 a curious arrangement of the lumen exists. Here there is 

 developed either an irregular chamber partly divided by columns 

 or islands of protoplasm, or else, and more frequently, an ir- 

 regular branching and looping of the lumen, one form of which 

 is shown in Fig. 35. The walls of the living tubules of this 

 region exhibit evident radial striations passing as dark lines 

 from the lumen to the external surface of the cells (Fig. 35). 

 Sections across the four tubules, the irregular windings of 

 which make up the greater part of the terminal loops of the 

 nephridia, especially at points where their approximation 

 enables us to readily compare their appearance, show a slight 

 difference in the structure of their cell walls. In the case of 



