166 THE C(ELOM AND NEPHRIDIA OF PALJ]MON SERRATlTS. 



fig. 3, the epithelium is less flattened, and the cells exhibit traces of 

 striation, especially towards their peripheral extremities ; the nuclei 

 in this region also staining deeply, and presenting a more or less 

 homogeneous appearance. In all parts of the bladder the nuclei 

 frequently appear, in preserved specimens, to project more or less 

 beyond the cell-protoplasm into the lumen of the organ. 



Grobben is of opinion that the bladder of P. Treillianus receives 

 only a single nephridial tubule, which by its convolutions builds up 

 the whole glandular substance of the kidney. In P. serratus a con- 

 tinuous series of sections shows that several tubules open into the 

 bladder. In the series from which the drawings figs. 2 a,b,c were 

 made, one such tubule is seen to open into the bladder in the 

 section a, while ten sections below this point, in fig. 2 b, no communi- 

 cation between the bladder and the renal tubules is visible. Groing 

 still farther back, however, the section fig. 2 c shows a second 

 opening, receiving a tubule which itself receives a number of branches. 

 These figures suffice to demonstrate the existence of two openings 

 into the bladder, and in the series from which the drawings are 

 taken, five such communications could be recognised. 



The course of tho tubules in the substance of the gland is exceed- 

 ingly hard to follow. All the tubes except one seem for a short 

 distance after their exit from the bladder to run parallel with the 

 surface of the gland, and then to bend inwards and upwards toward 

 the end-sac. During their course they give off numerous caeca 

 branches in the manner described by Grobben, One tube runs from 

 the bladder along the posterior edge of the gland, and passes for 

 some distance beyond the others ; it then turns upon itself and 

 passes into the substance of the gland, giving rise to a projecting 

 process, attached to the postero-external angle of the organ (see 

 fig. 1.) 



Immediately after leaving the bladder, the lumen of the tubules 

 is large ; they are lined by an epithelium exhibiting the charac- 

 teristic striation, and provided with a delicate cuticle. The nuclei 

 of the epithelial cells are coarsely granular in stained sections, the 

 granules staining fairly deeply. As it passes inwards, the lumen 

 of each tubule becomes smaller, and the nuclei become clearer, and 

 less distinctly granular. The two kinds of epithelium are shown in 

 figs. 4 and 5. 



The tubules are packed tightly together in the body of the kidney, 

 the small spaces between them being filled with branched connective- 

 tissue cells. 



On reaching the dorsal surface of the oi^gan, the renal tubules open 



into the " end-sac,^^ which has been already referred to,^ In fig. 



* A quite similar case, in which commuuication between the end-sac and the body of a 



