167 



which, apparently, has heen deposited gradually by the floiving 

 plasmir, layer, so in small quantities at the time — is exclusively 

 formed by fine carmine grains, captured by the choanocytes and 

 then passed on to this layer, or by coarser particles, which remained 

 sticking ivhen entering the prosopyles and then have been carried 

 off by this plasmic layer (p. 156). Probably both is the case. 



That in this way particles, which block up the prosopyles and 

 are of no food value, are removed as soon as possible from the 

 canal system, is very well conceivable and of much importance 

 to the sponge. So here we get to know a very powerful system 

 of cleansing the sponge: coarse particles, which, having passed the 

 ostia, remain sticking in the prosopyles and threaten to block them 

 up permanently, are taken up by the plasmic layer and are carried 

 off to a point in the tissue someivhere in the neighbourhood, from 

 where they are soon ejected into the excurrent canals, to be removed 

 with the ivater current {Fig. 73). 



On the other hand it is hardly to be accepted that coarse 

 particles from the water, which might be of use as food, should 

 be ejected in this way without any reason. But then one has to 

 suppose, that the sponge knows to decide whether a captured 

 particle contains nutrition or not, in the short distance between 

 taking up in the plasmic layer and delivery at the deposit of 

 feces. This seems very unlikely to me; the more so, because 

 above we have stated several times (p. 146 — 148, 157 — 158) that 

 carmine, most certainly, is carried into the sponge tissue and is 

 moved on for digestion to the amoebocytes with green symbiotic 

 algae, to be expelled only later on (p. 161 — 164). So it proves, 

 that only the amoebocytes with symbiotic algae — which are 

 performing the function of digestion (p. 157) — decide about 

 food or no food with regard to the particles captured. Consequently, 

 one may consider it as excluded that the same could also happen 

 already near the flagellated chamber. 



The explanation of the phenomenon, that on the one hand the 

 sponge carries the carmine even into its amoebocytes, while on 

 the other hand it disposes of a very rapid method of getting rid 

 of it immediately, seems to me the following : With a relatively 



