107 



easiest in consequence of the fact (point II, 3, 5, 6), that the 

 green algae in a sponge in darkness die in such a great number, 

 in light on the contrary only in such a small. Against the 

 opinion, that stronger „killing from want of food", so the in- 

 creased want of food, in darkness (point I, 1) would be a 

 cause for the manifold -dying, tells : 



a. The fact that, as appears from Table 8 and Table 15, several 

 of the (green) sponges, which have become almost colourless in 

 dark, contain only few food vacuoles, so behave as if they did 

 not specially want food, as stated on p. 97 — 98 (see ni's 333, 334, 

 340, 344, 3661, 366 II). 



h. The fact, mentioned on p. 94 sub 19, that there are about 

 the same number of food vacuoles in green sponges after their 

 culture in aquaria in light as in darkness ; in other words : that 

 the want of food would not be larger in sponges in darkness 

 than in those in light. 



By these facts the chief argument, that „killing from want of 

 food" could in general be a cause for *the dying of the green 

 algae in the amoebocytes (p. 106), would fall. 



With a view to this we would do better to exclusively admit 

 as cause for the dying: „poisoning" of the algae by products of 

 metabolism present in the amoebocytes, stronger in the dark and 

 active in all cases when for some reason the power of resistance 

 of the algae has weakened (p. 103, point I, 2, p. 106). 



On the other hand, however, there are even more and stronger 

 arguments which speak for the fact, that „killing from want of 

 food" (p. 103, point I, 1; p. 106) certainly must be a cause for the 

 dying of the algae in the sponge. I therefore refer to the points 

 II, 7 and 4. That increase of the mortality of the algae, when 

 the green sponges are transported into water from the conduit (in 

 light) — where the sponges will have to miss many food ma- 

 terials, which they found in nature, so that they will have to 

 make up for it in some way or other (see p. 97) — shows 

 very much in the direction of „killing from want of food". But 

 point II, 4-, the fact namely, that the mortality in weak con- 

 centration of the algae in the sponge in the light is equal to that 



