74 



the excretion of iron is concerned, Jordan is certainly right; 

 the presence of uric acid however, a very important excretion 

 product in lower animals, in the radial sacs of Asterias, in 

 the coeca of Aphrodite etc. makes me believe, that this ques- 

 tion is not yet completely settled, the more because Roaf 109) 

 found creatinine to be present in many of these organs. This 

 fact seems to me to need further confirmation, considering the 

 fact that this substance only rarely occurs in lower animals; 

 if it appears to be true, however, it is another indication in 

 the same direction. 



2. The function of the so-called siphon in the urchins has 

 never been investigated and is still completely unknown. The 

 assumption of Perrier 99), that it might have respiratory 

 function, does not seem very probable to me, because at least 

 in the species I have studied, one never observes any active 

 movements in them ') and because other organs of respiration 

 are known in Echinoidea. 



A priori it might be thought of as an organ of resorption. 

 This is not probable however for two reasons r 1 . its histology 

 is more primitive than that of the main-gut — see the 

 chapter on the histology — , 2. in sections of guts of animals 

 which had been fed on ammonium carminate and other sub- 

 stances I always found these substances present in large quan- 

 tities in the main-gut. 



Thirdly, one might assume that it is a kind of hydrostatic 

 apparatus for the transport of the food in the gut. The food 

 is in our sea urchins transported in round masses, included in a 

 mucous membrane — food-vacuoles as observed already by 

 Roaf and Scott; see p. 33 ^. They fill the whole gut and 

 owing to the incompressibility of fluids, it becomes necessary 

 to have a device of some kind to permit their forward move- 

 ment, the siphon might serve for this purpose. 



22. THE RESORPTION FROM THE 

 PERIVISCERAL FLUID. 



When we take for granted that the perivisceral fluid has the 

 function of „blood", of distributor of food substances, it seems 

 very strange that we never find these substance in it. In the 

 chapter dealing with this liquid we have seen that it contains 

 almost no organic substances, except for a small quantity of 

 uric acid and some corpuscles. Ordinarily no monoses, no amino- 

 acids nor peptones nor proteins are present. 



In the chapter on resorption in Echinoidea and Holothurians 

 we have learned that after the artificial ingestion of pure food 



') V. Henry 53) however saw rhythmical contractions. 



