and external circular fibres with on both sides a layer of con- 

 nective tissue. In the outside layer we find the so-called mar- 

 ginal vessels, at the inside the general lacunar system and many 

 nerve fibres. 



In some places of the intestinal wall the peritoneum leaves 

 an open space of ellipsoid form, bringing the external connec- 

 tive tissue (and with it the marginal vessels ?) in contact with 

 the coelom, a so-called ,, button" (Herouard). By them the 

 marginal vessels communicate with the general lacunar system 

 and here the circular musculature is perforated. 



The cells of the epithelium are very long and have cylindrical 

 shape. They are covered with a fairly thick cuticula and show 

 two types. Many cells sho^vf a fine granulation and appear to 

 be secreting cells ; others have the character of mucus cells. In 

 pharynx and cloaca we find normal epidermis cells. 



Note. Of special interest is the presence of amiboid migra- 

 ting cells probably of mesodermal origin-though F r e n z e 1 denies 

 this- in the visceral epithelia of all Echinoderms. Biedermann 

 in Winterstein's Handbuch 136) emphasises this point particu- 

 larly. Frenzel 41) already found numerous red migrating 

 cells in the normal epithelia of Toxopneustes and Spatangus, 

 which he calls „rothe Wanderzellen". The color of their guts 

 is very different in different circumstances and physiological 

 conditions. In the same species of Toxopneustes f. i.. Frenzel 

 found the gut in one case black, at another time pink with black 

 spots, sometimes again the whole gut reddish-brown. This 

 partly accounts for the difference in color of the gut as a whole. 

 St. Hilaire 112)') also observed them and found the same, 

 cells present in the perivisceral fluid. C o h n h e i m and Cue- 

 not found the same thing and found the protein crystalloids, 

 studied bij List 81) and a fatty substance present in them. 

 Are they carriers of food? Most probably not, because they 

 only move towards the , lumen, as Frenzel himself states. 

 Possibly they carry excretion-products to the lumen of the gut ; 

 this is rather probable from their movements which can even 

 be observed in vivo according to Frenzel. Enriques 37) 

 brings them in connection with the peculiar enzyme secretion 

 described by him in Holothuria tubulosa. According to him 



') Saint Hilaire makes a sharp distinction between the ,, granular cells" 

 and the ..phagocytes". The granular cells according to him do not have any 

 phagocytical activities; they are so to say ..unicellular glands", formed in the 

 peritoneal epithelium and dying and dissolving in the intestinal lumen. They 

 do not participate in the clotting process and do not play a role in digestion : 

 they are neither „Fermentzellen", nor phagocytes, neither do they contain any 

 reserve substances. They should take care of the excretion by taking up foreign 

 substances from the surrounding fluids, storing them as granulae and carrying 

 them through the gut-wall. 



