46 



VII. The intrinsic amount of the various green and 

 colourless stages of the „symbiotic" algae in sponges. 

 The factors ruling this amount. How green and colourless 



sponges keep up their „colour", and how they arise 

 from each other. 



a. 



We now have stated the nature and origin of the colourless 

 symbiotic algae, and resume the discussion started in chapter Y. 

 We put the questions: What is a green sponge, what a colourless 

 one; how do they keep up their „colour", and how do they arise 

 from each other? 



For the present we might answer the first two questions as 

 follows (pag. 35, Table 6) : Green sponges are sponges containing 

 a great number of living green algae and a smaller number of 

 dead colourless algae ; colourless sponges are sponges containing 

 a small number of living green algae and a greater number of 

 dead colourless ones. But tre should now compare the green 

 sponges — usually occurring in light, as we know (p. 35) — and 

 the colourless ones — usually occurring in darkness — more 

 accurately as to their intrinsic amount of the various (green and 

 colourless) stages of the symbiotic algae; especially newly caught 

 sponges. 



To that purpose I analyzed, as mentioned on p. 35, a great 

 number of those Spongillidae, green and colourless ones, Spongillae 

 as well as Ephydatiae (Table 6 A, C) ; the amount of algae in 

 Spongilla was examined separately in tissues in diflFerent stages 

 of development: in very young tissue, in full-grown, and in 

 tissue at rest (gemmulae). The number of the algae mentioned 

 always concerns the amount present within an equal volume of 

 each sponge. The results of the analyses are as follows: 



1. Green as well as colourless symbiotic algae occur in the green 

 sponges i?i, light as well as in the colourless ones in darkness. 



2. In the course of the development of the tissues of the green 

 Spongillae the number of the green algae remains constantly con- 



