64 



from an isotonic solution by theintestinal wall (Jordan 69))-— 

 may give us the key to the explanation of this phenomenon as 

 yet unexplained on a physico-chemical basis. Such instances 

 as Helix may be especially instructive, their gut epithehum does 

 not take either iron, carmine or fat. These properties have 

 also been considered as characteristic for resorbing epithelia 

 (Cuenot. Arch, de Zool. exp. et gen. (3). 25. 1899. 7; 

 Biedermann and Moritz 9)). 



Among the many, perhaps unrehable, results of Cohnheim, 

 one is very interesting. If sugar is injected into the perivisceral 

 fluid, he finds it back inside of the gut. I have made similar 

 experiments, using cane-sugar for the injection. Two interesting 

 facts could be observed in such animals : 1 . If the gut contents 

 were secured after about eight hours and hydrolysed, a strongly 

 positive Fehling's test indicated the presence of sugar; 

 this proves that Cohnheim did not make a mistake in his 

 observation, 2. Some of these animals showed a peculiar sweUing, 

 as though they had taken up water to compensate for the exces- 

 sively high osmotic pressure of their coelomic fluid. This phe- 

 nomenon was not observed regularly, but was very striking. 

 It even attracted the attention of some visitors to the laboratory. 



The first result is interpreted by Cohnheim as proof in 

 favor of his conception of the gut wall as diffusion-membrane. 

 I am inclined however to believe that another explanation is 

 more probable and I was glad to find that E n r i q u e s had made 

 a remark of the same kind. In our chapter on excretion 

 we shall see that uric acid, a normal excretion product of the 

 Echinoderms, is excreted into the lumen of the gut. Probably, 

 as we shall there see, this is the normal way of excretion in 

 this group, which is certainly true in many other invertebrate 

 groups. The same thing may hold true for sugar, the excess 

 of non-utilisable sugar — see the chapter on enzymes in the 

 perivisceral fluid • — being possibly excreted here, just as in mam- 

 mals in cases of alimentary glycosuria. 



The swelling phenomenon then might be explained by the 

 assumption that the animal is not capable of „working through" 

 so much sugar at once but is capable of taking up water by means 

 of its many water-permeable membranes. In that way a pre- 

 liminary dilution would make the high osmotic pressure less 

 harmful. Since I could not study this problem more in detail, 

 I shall leave this explanation in a very hypothetical form; the 

 recent work of Dekhuyzen 30), however, on the Sipuncu- 

 lidae makes such hypothesis rather probable. 



Note. Enriques has kept some of his Holothurians in a 

 vessel filled with sea water containing milk. After some time 

 he finds fat droplets in the animals blood-vessels and later on 

 in its perivisceral fluid. StiU later the quantity of fat in the 



