108 



in strong concentration (per unit of sponge volume) can even 

 only be explained by this last cause for the dying. From this 

 would follow, that a sponge in light, whether it lodges many or 

 few green algae, wants one and the same number of these for 

 food. It is quite clear, why (II, 4) in a sponge in darkness the 

 mortality in weak algal concentration is less than in a strong 

 concentration : in darkness the mortality is much larger than in light ; 

 if however the concentration is weak, it is impossible that many 

 algae die. Why (II, 2) the mortality in all stages of development 

 of the tissue remains constant, could be explained by „killing from 

 want of food" as well as by „poisoning by products of metabolism". 



Finally there are arguments which show, that in sponges in 

 darkness there is certainly reason to speak of an increased want 

 of food — in consequence of lack of 0.^ — ; which would make 

 a stronger „killing of the algae to digest" from the side of the 

 sponge cells quite intelligible (p. 103, point I, I, p. 106): 



(X,. The argument, mentioned on p. 97, that in colourless Spon- 

 gillae from darkness, eicamined when newly caught, the number 

 of food vacuoles appears to be greater than in green ones from 

 light (p. 94, point 21) ; which argument formed exactly the 

 starting point for the supposition about the changed katabolic 

 phase in lack of O2 (in this case = lack of light) (p. 98). 



/3. When speaking about the growth of the sponges, I have 

 mentioned (p. 53) that one could generally state, that green 

 Spongillae (in light) are larger, so grow more quickly, than co- 

 lourless ones (in darkness). What can be the reason? Very likely, 

 there is no question of a stronger nutrition of the green sponge 

 from the side of its green algae, while even somewhat more algae 

 are digested in the colourless sponge than in the green one, as 

 mentioned on p. 97. Consequently, there is no question about, 

 that the difference in rapidity of growth is founded on a smaller 

 quantity of food, which the colourless sponge would have at its 

 disposal. But it will have to be founded on a greater want of 

 food, namely chiefly of proteins, in consequence of lack of suffi- 

 cient O2 in the tissues of the colourless sponge in darkness 

 (p. 98, 103, I, 1 and p. 88). 



