96 



here the question, if this supposition — the Putter theory (48, 

 49) — should also count more or less for the Spongillidae ; for 

 these sponges possess, as we will see presently, another very rich 

 source of food ; so that the argument, on which Pütter's theory 

 is based, seems not to hold good for the fresh-water sponges. 

 The dissolved organic materlals of the lake water are for them 

 surely not the most important source of food. 



Next one might have thought, that it were the products of 

 photosynthesis of the green symbiotic algae (the oildroplets and 

 carbohydrates) which, after having been ejected by the algae, would 

 serve the sponges as food (point 1, 3, 11, 12). We now know^ how- 

 ever (point 5, 13), that it is very likely such an eject'mg of oil- 

 droplets and carbohydrates by the algae does not take place at all. 



There is still another possibility, viz. that the sponge is fed by 

 proteins (or their constituent parts) which the green algae could 

 eject. For the (colloidal) proteins this sounds, however, very un- 

 likely ; and also for their parts, the amino acids, will be no 

 question about ejecting by the algae, as we saw above that it is, 

 very likely, already not the case for the primary products of pho- 

 tosynthesis (the carbohydrates), that are still much more numerous. 

 Consequently, nor in this way we escape from the difficulty. 



The solution is, that according to point 22 — 24 (p>. 94 — 95) 

 the sponge has a very important, almost inexhaustable, perhaps even 

 its principle source of food in the green symbiotic algae, which con- 

 tinually die (p. 46' — 48, 57) free in the protoplasm of its amoebocytes, 

 and ivhich then pass there gradually from „colourless algae ivith clear 

 structure'''' into the successive „solution stages'\ „colourless ones with 

 shade of structure'''', „colourless ones tvithout structure", and „vague 

 shades of colourless algae", in order to finally disappear entirely 

 (p. 42 — 45). Consequently, here free in the protoplasm of the amoe- 

 bocytes necessarily an — dlthough rather slow (p. 57),nevertheless — 

 complete break-down and solution takes place of the substances the 

 symbiotic algae consist of; ivhile the products of the decomposition 

 must come to the disposal of the amoebocytes. How this decom- 

 position is produced, I cannot yet decide ; but it is evident, that 

 enzymes of the amoebocytes will take part in it. 



