49 



E. the niultiplication of the green algae within the tissues 

 (the factor of multiplication). 



F. the mortality of the green algae within tlie tissues (the 

 factor of mortality). 



I shall now treat each factor separately. 



A. The factor of import. 



As I mentioned above (pag. 28), it is possible to durably 

 transmute colourless sponges into the green form by placing 

 them into a diluted suspension of isolated green symbiotic algae 

 in water, I give a more detailed description in Table 7. There 

 we see, that a living colourless Spongilla (volume 3 — 10 c.M^) 

 is able to make perfectly clear within a few days 3 litres of a 

 grayish suspension of algae, by which the colourless Spongilla it- 

 self grows light-green; and that the rapidity of this process is 

 directly related to the number of oscular tubes, the sponge shows. 

 As we know from the research of Vosmaer and Pekelharing 

 (62), these tubes accelerate the rapidity of the water current 

 through the sponge body — serving as lengthening pieces of 

 the draught canals — . Therefore we may conclude that, the 

 quicker the current in the canals of the colourless sponge, 

 the more quickly the sponge will gei clear — so to say by 

 filtering — the troubled suspension, and itself will grow light- 

 green by capturing the green algae. The oscular tubes are not 

 indispensable, of course — as was proved — ; the current of 

 water can also go on, when they are lacking. One might think it 

 possible, that the sponge does not only catch the algae within 

 its tissues, they have got into by the current, but also at its outer 

 surface. This possibility might be realized; but it can hardly 

 come into consideration in comparison with the first method of 

 capturing, as I will point out afterwards in chapter B and C 

 (on the current of water and the ingestion of food). I will only 

 mention now that the algae are soon joined quite normally 

 within the sponge amoebocytes (not vacuoles!), and that the light- 

 green colour of the sponges, after they have been transported 

 into daylight into aquaria filled only with water from the con- 



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