23 



seems to be wrong. Jordan could show this by folding a prey 

 in blotting paper; this prey was broken down just as well 

 though. less vigorously. 



' One of the first authors who clearly realised the importance 

 of this way of digestion and understood it as the phylogenetic 

 precursor of the process in higher organisms, was E 1 i'e 

 Metschnikoff 84)- in his paper on intracellular digestion in 

 coelenterates. The epithelium of the coelenteric cavity of these 

 animals may be called an amiboid epithelium, in some species 

 (e. g. Praya diphyes, a Siphonophore) a true plasmodium is 

 even formed. In Ctenophores the food is carried further into 

 the body by mesodermal cells, as in Sponges. 



An excellent monograph on the intracellular digestion in the 

 flat-worms has been given by Saint-Hilaire 113). The food 

 taken by these animals is found as such in the cells of the 

 lining of the gut. Blood-corpuscles f. i. keep their characteristic 

 shape and only later they are gradually broken down- The 

 products of digestion are collected in special vacuoles and 

 deposited there in the form of crystalline structures. Numerous 

 cell-inclusions appear to grow at the expense of the food as 

 it is broken down. ') ~ 



In the ..higher" animals conditions are totally different. 

 Apart from the Gastropods (Enrique s, Biedermann and 

 M o r i t z) digestive phagocytosis has been observed in no group 

 of the higher animals. Digestion has become an extracellular 

 act : it takes place in the „interior exterior" and it is doubtful 

 whether in the resorption the separate protoplast plays a role 

 as such. Here the free enzymes are not, as in the Actinians, 

 a preliminary adaptation, a „Hilfsmechanismus", but the very 

 essential thing in digestion. 



In snails we find a kind of transitory stage. The so-called 

 „liver" of these animals („Hepatopankreas"), has become an 

 organ of special interest since the investigations of Bieder- 

 mann and Moritz. In the digestive juice of the represen- 

 tatives of this group all enzymes — up to a cytase studied 

 specially byAlexandrovicz 1)^ — are found free except for the 

 proteolytic one. The proteolysis is localised in the liver. Protein 

 is actually digested, as a careful analysis of the faeces and the 

 food^N shows ; fibrin is not digested however, if treated with 

 the stomach fluid or with a watery extract of the liver. A free 

 acid is formed, as we will mention in chapter 17, the whole 

 mass becomes gelatinous, but no „digestion" takes place. Com- 

 pletely different is the result however if the shreds are placed 

 between two cut surfaces of the liver. In less than no time it 



^) 1 . Even a vacuole is not always necessary, as le Dantec showed 



for Gromia and Pfeffer for Myxomycetes in the case of crystals of asparagin. 



2. Excretion also takes place by the same epithelium in many of these forms. 



