145 



Many times I have observed this phenomenon of carmine cap- 

 turing, in different preparations during several years (1915, '16 

 .and '17); it always took place in the way described here. I had 

 also the opportunity of demonstrating it to Professor Vosmaer and 

 Professor Pekelharing; both held my conception convincingly 

 proved by the living preparations. 



In exactly the same way as described now for carmine, I have 

 also observed several times green symbiotic algae being captured 

 by the choanocytes in a chamber. 



As mentioned before, only very seldom a carmine grain gets 

 into the zone of the collars, as most of them have generally been 

 captured already in advance. If it does take place, however, it 

 is the collars which prevent their escaping. For these appear to 

 be very active enlargements of the capturing-surface of the choano- 

 cytes, as the particles which might have escaped from their cell- 

 bodies or collar-bases are, in most cases, held between the long 

 collars, as I have been able to observe. A representation of such 

 a case is to be seen in Fig. 67, a carmine grain which I saw 

 captured between 3 collars (seen from above). Afterwards one 

 can see the grain slowly descending along a collar to the base. 

 (Fig. 68, 1-2). I saw the same thing happen to green symbiotic algae. 



So here we have stated the remarkable fact^ that the choanocytes 

 capture the food particles in exactly the same way as the Choano- 

 flagellata. 



Only very rarely a carmine grain quite succeeds in escaping 

 from the collar cells; then one sees it slip through the chamber. 

 Sometimes also, the way, gone by a grain in the chamber be- 

 fore being captured, seems different from the normal one; an 

 explanation might be given for it, but cannot be proved. 



Now the prosopyles still need treating. They are generally not 

 to be distinguished, even if one sees the carmine grains enter 

 the flagellated chamber at a certain point; and no wonder. For 

 one does not see the separate collar-cells either, but only their 

 joined layer as a whole. So it may count as a peculiarity, that 

 there were even two prosopyles to be distinguished in the chamber 

 of Fig. 66. The left one was varying in width; I measured it as 



