OF PERIPATUS CAPEXSIS. 90 1 



The narrow part is lined by small epithelial cells, which are 

 directly continuous with and perfectly similar to those of the 

 epidermis (fig. 20). It is provided with a superficial coating 

 of longitudinal muscular fibres, which thins out where it passes 

 over the sack, along which it only extends for a short distance. 



The sack itself, which forms a kind of bladder or collecting 

 vesicle for the organ, is provided with an extremely thin wall, 

 lined with very large flattened cells. These cells are formed of 

 granular protoplasm, and each of them is provided with a large 

 nucleus, which causes a considerable projection into the lumen 

 of the sack (figs. 20, 29 j). The epithelial wall of the sack is 

 supported by a membrana propria, over which a delicate layer 

 of the peritoneal epithelium is reflected. 



The coiled tube forming the second section of the nephridium 

 varies in length, and by the character of the epithelium lining 

 it may be divided into four regions. It commences with a region 

 lined by a fairly columnar epithelium with smallish nuclei (fig. 

 28 s c i). The boundaries of the cells of this epithelium are 

 usually very indistinct, and the protoplasm contains numerous 

 minute granules, which are usually arranged in such a manner 

 as to give to optical or real sections of the wall of this part of 

 the tube a transversely striated appearance. These granules are 

 very probably minute balls of excretory matter. 



The nuclei of the cells are placed near their free extremities, 

 contrary to what might have been anticipated, and the inner 

 ends of the cells project for very different lengths into the inte- 

 rior, so causing the inner boundary of the epithelium of this 

 part of the tube to have a very ragged appearance. This por- 

 tion of the coiled tube is continuous at its outer end with the 

 thin-walled vesicle. At its inner end it is continuous with region 

 No. 2 of the coiled tube (fig. 28 s c 2), which is lined by small 

 closely-packed columnar cells. This portion is followed by 

 region No. 3, which has a very characteristic structure (fig. 

 28 s c 3). The cells lining this part are very large and flat, and 

 contain large disc-shaped nuclei, which are usually provided 

 with large nucleoli, and often exhibit a beautiful reticulum. 

 They may frequently be observed in a state of division. The 

 protoplasm of this region is provided with similar granules to 

 that in the first region, and the boundaries of the cells are usually 



