150 



an apparently undifferentiated plasmic substance (in which few 

 or no symbiotic algae) lining the canals. A lively transport of 

 carmine takes place there. By itself this does not say anything; 

 that carmine could be proceeding from the flagellated chambers, 

 though then it would be rather peculiar that it should exclusi- 

 vely extend along the canal walls. Sometimes, however, it also 

 appears that there is a certain difference in size between the 

 carmine grains (not conglomerates!) within the choanocytes and 

 those in the canal walls. The former are almost exclusively small 

 (0.5 — 0.7 /C^), those in the walls often much larger (1.5 — 4 f^t,). 

 This fact now is supported and completed in a very desirable 

 manner by what we could state above under 2 in ravel prepa- 

 rations. 



The 3 points mentioned sufficiently indicated, that in a sponge 

 had to be still quite a different method of capturing food-particles 

 — and especially coarse particles — ; and such in the canals 

 themselves^ outside the flagellated chambers ; for wich then, of course, 

 only the incurrent canals had to be considered. By chance I dis- 

 covered that method; though, after all, one must say that it had 

 to be functioning in a sponge. 



Just think of the structure of the canalsystem : incurrent canals — 

 flagellated chamber — excurrent canals. One always used to say that 

 the narrow ostia (dermal-pores), placed at the entrance of the 

 incurrent canals, prevent the too large particles floatiiig in the 

 water from entering, and so from blocking up the canal system. 

 But these ostia measure in living Spongillae, as I have been able 

 to state several times, even to 63 X 84 fz, while Delage (14, 15) 

 could fix their width in killed Ephydatiae on 6 — 30 f/.. Now, 

 generally the prosopyles only measure, as we saw, 3 — 4 f/.. So it 

 goes without saying that numbers of particles will enter by the 

 ostia, which are too large to pass the prosopyles. What must hap- 

 pen to these particles, what must the sponge do with them, when 

 they have come with the water-current to a flagellated chamber 

 and remain sticking in a prosopyle, so stop it up? They must 

 be removed, otherwise — in nature there are so many particles 

 in the water — the sponge would unavoidably die within short, 



