72 



In this way we find that^ if in nature a sponge containing an 

 arbitrary small number of green algae^ so a more or less colour- 

 less sponge, which was grotving in darkness and kept up its colour, 

 is transported into daylight, it must unavoidably accumulate a 

 large quantity of green algae in its tissues and therefore become 

 dark-green' itself, espjecially in consequence of a strongly increased 

 multiplication and a much decreased mortality of those algae in 

 light. When the whole tissue is crammed tvith green algae, the 

 various factors ruling their number change in such a manner, 

 that a 7iew balance is established ; these changes are an increase 

 of the growth of the sponge and perhaps also of the export of 

 green algae. 



(I have always put the export to account. It is, however, an un- 

 certain factor, as I have stated. One may therefore leave it out 

 entirely. That would be of no consequence to the argumentation). 



Up to now my argumentations have set forth from sponges, 

 vrhich kept up their colour and, therefore, showed the equation 

 of balance for the number of their green algae (p. 68). But the 

 same can be proved for sponges changing their colour : as we 

 proved that a dark-green sponge from light becomes colourless 

 in darkness, it is a matter of course that a sponge, which grew 

 green or colourless in light (therefore, a still more or less light- 

 green sponge) must also become colourless in darkness; while the 

 reverse will be the case for sponges, which were growing colour- 

 less or green in darkness, and were then transported into day- 

 light. The questions, why in general a green sponge in light 

 remains constantly green, and a colourless one in darkness con- 

 stantly colourless {i + r + mu = e -\- g -\- mo), have in fact been 

 answered already above under B and A (pag. 69 — 72). Also other 

 questions may be proposed and answered in the same way. 



We have stated tiow, that (and why) generally in nature 1. sponges 

 in darkness must become colourless and sponges in light green, 

 2. green sponges in light and colourless ones in darkness must 

 keep up their colour. 



