THE PHYSIOLOGY OF EXCRETION. 105 



canal system is also useless matter which the nephridial cells 

 secrete and empty to the outside together with the excretory 

 granules. 



There is only one more point to speak of, namely, the sig- 

 nificance of the peripheral organs (Fig. 13). We must consider 

 that the nephridial cell has an extremely complex function. It 

 has to respire, to assimilate and regenerate its protoplasm, and 

 to discharge the excretory products which are formed during 

 its own metabolism, like any other cell. In addition to these 

 functions, the cell has to secrete isolating substances around 

 the excretory granules, has to provide a mechanism for the dis- 

 charge of these substances, and has to nourish and regenerate 

 this mechanism. Finally, it has to provide fresh oxygen for 

 the sustenance of the 

 peristaltic motion of 

 this mechanism. I 

 think it possible that 

 the peripheral organs 

 may have something 

 to do with the provi- 

 sion of fresh oxygen; 

 that they are, per- 

 haps, the means of 



FIG. 13. 



communication be- 

 tween the cell and the surrounding tissues, stimulating the 

 latter to give up oxygen for the benefit of the nephridial cell. 

 I present this merely as a suggestion, not being able at the 

 present time to form even a definite hypothesis as to the 

 purpose of these remarkable organs. 1 



We have now completed our task, having followed the paths 

 along which the excretory products are carried until they are 

 thrown out of the body, and also having studied all the changes 



1 During the winter following the delivery of this lecture, I succeeded in 

 finding similar peripheral organs in the ciliated funnel cells of the leeches, and in 

 the intestine cells of the same animals (which are likewise ciliated) and I have 

 come to the firm conviction that these specialized microsomes are the producers 

 of an oxidizing ferment (which ferment exists as we know) by which assumption 

 the last link in our metabolic circle is found. More about this point will be 

 published in another place. 



