No. 3.] THE DISCODRILID NEPHRIDIUM. 359 



9. General and Comparative. 



I regret that my own physiological and embryological studies 

 of the discodrilid nephridium are not sufficiently advanced for 

 publication at the present time. In a general way it may 

 be stated that the results of the former agree with the now 

 generally accepted notion of the excretory function of the 

 nephridium, but it is desirable that the special physiological 

 parts played by the several structurally distinct regions of the 

 tubule be determined. This nephridium stands in a twofold 

 relation to the excretory process. The first is a direct one, in 

 that the nephridial tubules eliminate, and finally deposit within 

 their lumina in the form of granules, waste matters contained 

 in solution in the coelomic fluid, which bathes them without 

 and passes in a constant osmotic stream through their walls. 

 This is indicated by the conspicuous radial striation and by the 

 presence of deposited granules within the protoplasm. This 

 has been shown by Benhani (e) for Lumbricus, and by several 

 other observers in allied genera. Of probably still greater 

 importance quantitatively is the passage of waste matters in 

 solution through the tubule walls into their lumina without 

 deposition. This is perhaps surmised rather than proved by 

 the fact that alcohol causes the appearance in the protoplasm 

 of abundant granules, before invisible, indicating their precipi- 

 tation from a state of solution. 



The second is an indirect relation, in that the nephridia serve 

 simply to conduct to the exterior of the body the products of 

 excretion elsewhere accomplished. The chlorogogue cells stand, 

 as has been frequently pointed out, in a most intimate relation 

 to the perienteric blood sinus, and also, by means of proto- 

 plasmic strands, to the absorptive surface of the alimentary 

 canal. The existence of strong diffusion currents through them 

 from the alimentary epithelium, and especially from the blood 

 sinus, to the coelom, is indicated by the arrangement of the 

 granules. These form lines extending from the haemal to the 

 coelomic surfaces of the cells, many of them curving around 

 the nuclei, as though these obstructed free movement in straight 

 lines. The cells are minutely and abundantly vesicular, and 



