83 



cytes eliminate dying mesodermal cells, and that they take up 

 all kinds of foreign bodies, dyes and bacteria, does not prove 

 that they are the only, or even the chief, organ of excretion. 

 Something of this nature is also done by the mammalian 

 leucocytes, and yet they are not considered to take care of 

 excretion. This is especially true in cases where foreign bloods 

 or pathogenic bacteria are injected. 



The same thing has already been pointed out for the cases in which 

 these phagocytes take up food substances. Even if these are digested as in 

 the cases of injection of starch or oUve oil emulsions, this does not prove 

 that they play a role in the natural process of digestion. 



The possibility that the „liver" plays a role in excretion, has 

 already been discussed in chapter 21. 



Not satisfied with the little evidence known about excretion 

 in our group, I made some experiments of my own on this 

 problem which have led me to absolutely different conclusions. 



In our study of the perivisceral fluid we have seen that it 

 is nearly the same as sea water, except for a small quantity 

 of uric acid which discloses itself when the fluid tested by 

 means of Folin's uric acid reagent. This substance is always 

 present though in varying concentrations and in all three of 

 our species. This proves that is a regular waste product in their 

 metabolism. 



The next step was to find out in what way it is ehminated. 

 Faeces of Arbacia were collected, shaked with destilled water 

 in a test-tube, then the liquid was filtered. In the filtrate Folin's 

 uric acid test always gave positive evidence, in a few cases the- 

 color was rather faint, but generally it was strongly positive. 



The same material proved to be present in the rectal coeca 

 of Asterias. It is difficult to isolate these organs as they are 

 very small and lie in the neighborhood of the anus. The whole 

 stomach of the starfish is rather fragile, but the rectal part always 

 sticks to the dorsal tegument. This consists not only of the 

 rectal coeca, but also of a part of the rectum. The whole mass 

 was simply taken as such and extracted with cold destilled water. 

 This extract after having been filtered, showed the same typical 

 blue coloration. 



In looking up the literature on the subject I found a paper 

 of Griffiths 48) in which the same uric acid is reported to 

 be present in the five pyloric coeca of Uraster rubens, a fact 

 which I mentioned in the chapter on the function of these organs. 

 He examined chemically and microchemically the secretion of 

 the five stomach pouches and the radial sacs and came to this 

 conclusion from the following evidence: 



1. Treatment with NaOH gives a flaky precipitate. Crystals 

 of various forms appear to be present. If treated with alcohol, only 

 rhombic crystals are found. With HNO3 they give the murexide test. 



