25 



and even continued digestion does not give any evidence of 

 the presence of amylolytic enzymes in free form. 



Strange enough the same thing is true in many cases if cane 

 sugar is used as a substrate. In the previous chapter we have 

 seen that an invertase is certainly present in the representatives 

 of this group. It could however not be proved so readily that 

 this enzyme is present in free form, in Thyone I only got one 

 positive result on six tests, in Arbacia one on five '). In Asterias 

 no positive evidence was obtained. 



I am at a loss for an explanation of this fact. Maybe it 

 means that there is a certain periodicity in the enzyme secretion. 



For experiments of the same nature on fat I refer to the 

 chapter on the digestion of fat. 



When we look over the general result of these experiments, 

 we see that those enzymes which are present in the watery 

 digests, are (occasionally) found in free form. 



On the other hand: the enzymes present are rather weak; 

 we will be more impressed of this fact when we come to 

 consider the gut-contents of Thyone and the faeces of Arbacia. 



The mucous membrane in which the food is included in the 

 digestive juice of the sea-urchins according to Scott 117) and 

 Roaf 108), is other evidence in favor of the occurrence of 

 free enzymes. These membranes are sometimes formed already 

 in the first part of the gut, mostly however later on. In such 

 conditions there is no possibility of phagocytosis or anything 

 of the kind; digestion and resorption must take place in and 

 from this food-vacuole. 



Whether or not phagocytosis plays a role in the digestive 

 processes of our group, is hard to decide. I started the present 

 investigation with the idea of finding very primitive conditions. 

 For this reason I made many experiments in which I fed 

 urchins or starfishes on suspensions of carmin or bone-black. 

 In the large amount of material collected from such animals 

 I found but one section in which the grains of carmin could 

 be seen lying inside of the cells (Fig. 3 of our colored plate). 

 One positive experiment of this kind of course does not prove 

 much ; a closer investigation of the importance of phagocytosis 

 in the digestion of the Echinoderms seems very well worthwhile 

 however. 



The fact that carmin is found in granular form inside of 

 the cells, does not always prove phagocytosis. H. Eisig SS*") 

 in the case of Capitella assumes, that carmin is absorbed in 

 dissolved form and reprecipitated in the cell-body. In fact no 

 other evidence whatsoever of phagocytosis was obtained. 



') Roaf also failed to find any evidence of the presence of a saccharase in 

 the Echinoidea. 



