68 



I. The question , why green as ivell as colourless algae oecur in 

 sponges in ligJit as icell as in darkness. Because in sponges in 

 light import, multiplication and dying of green algae takes place, 

 import and dying in sponges in darkness. 



II. The very important question, directly corresponding with 

 that of the foregoing pages, n-hy in nature a sponge in light 

 contains an excess of green algae^ consequently it is green; why a 

 sponge in darkness contains a small numher of green algae^ con- 

 sequently it is colourless; how a green and a colourless sponge 

 arise from each other. 



The data, we will make use of, concerning the factors of im- 

 port ') (ï) (pag. 50, 51), export (e) (pag. 52), reduction (r) (pag. 

 52 — 53), growth (g) (pag. 53), multiplication (mu) (pag. 55 — 56), 

 and of mortality (tiio) (pag. 60, 61) are printed in italics on 

 the pages mentioned here. 



I want to point out emphatically that all these data have 

 been calculated per unit of time and per unit of sponge-volume, 

 while the facts resulting from Table 6 (pag. 46 — 48, point 1 — 11), 

 which we have got to explain here, are also calculated per 

 same units. 



We now imagine a sponge (containing an arbitrary quantity 

 of green algae) keeping constant its colour, therefore its num- 

 ber of green algae. For this number the following formula 

 would be binding: 



« + r + mu = e -{- g -{- mo 



An equation of balance: the number of green algae added per 

 unit of time in the unit of sponge-volume continually counter- 

 balances the number which is substracted. Now we know that 

 in nature a (green) sponge in light as well as a (colourless) sponge 

 in darkness really keeps up its colour for a long time (pag. 35). 

 Consequently, this formula is binding for their quantity of 

 green algae. • 



1) If the import in green sponges in light might prove greater thaa that in 

 darkness (p. 51, note), the following argumentations would be binding a fortiori. 



