268 INVERTEBRATE PHYSIOLOGY 



present in coelomic fluid. It follows that, if the coelomic fluid contributes 

 only 1/16 of the volume of the urine, we have no real evidence for the re- 

 absorption of protein. But, if the contribution of the coelomic fluid is 

 more than 1/16, we are still not able to judge whether the protein was 

 absorbed in the nephridia or in the gut, into which the open nephridia 

 drain in this form. 



A different situation obtains in Lunibricus where the nephridia are 

 "open" but empty to the outside. If some test substance can be found 

 which leaves the coelomic fluid but does not enter from the blood, it may 

 be possible to work out the relative contributions from these two sources. 

 The substance should be one of large molecular weight and perhaps a pro- 

 tein would do. But it appears already that the native protein of the earth- 

 worm will not answer the question. Ramsay (1949a) found it convenient 

 to heat-sterilize samples of blood, coelomic fluid, and urine of Lumhricus 

 terrestris to be saved for later analysis. He noted that there was an abund- 

 ant coagulum from the blood but a slight or nonexistent coagulum from 

 urine and coelomic fluid. Quantative analyses for protein were not done 

 on the small samples which had been collected for other purposes. If the 

 protein content of the coelomic fluid in Lumbriciis is very low, then, again 

 on the partition hypothesis of the origin of urine from both coelomic fluid 

 and blood, a small difference in the protein concentration of coelomic 

 fluid and urine is to be expected and the amounts may be too low to answer 

 our question quantitatively. 



On the reabsorption of hemochromogen, on the other hand, Bahl's ex- 

 periments seem very satisfactory, and conclude what he found to be a long 

 labor. His discussion of earlier views of the function of the "ciliated 

 middle tube" cannot be repeated here. Suffice it to say that the brown 

 granules of the cells of this segment had previously been considered to be 

 guanine or urates, whereas Bahl demonstrates by solubility properties and 

 absorption spectra that the chief material is a hemochromogen. Because of 

 the small accumulation in young worms and the large accumulation in 

 adult worms, Bahl considers that this material is retired from service and 

 that these cells represent an example of the classical "kidney of accumula- 

 tion." A question might be raised as to whether or not a larger earthworm 

 might not have accumulated, and be turning over, a larger store of iron- 

 containing pigment. If this were so the reabsorption would be a useful, 

 rather than a nonuseful, one. Only rate measurements would answer this 

 question. A further question remains, however : Is the hemochromogen 

 accumiflated from the lumen side, having entered with coelomic fluid from 

 the nephridiostome, or has it been picked up by "athrocytic" activity from 

 the coelomic fluid bathing the outside of the nephridium? From Bahl's 

 observations it appears possible to call this accumulation a "reabsorption," 



