42 



What indeed may he the relation between these green and colour- 

 less algae? 



I refer again to Table 4 A, B. There we see that, when the 

 green algae decrease in number, the colourless ones increase (in 

 order to disappear after some time). Therefore it is probable, that 

 the green ones can become colourless. 



Next we should consider that, as green sponges grow colour- 

 less in darkness (pag. 35), which goes together with a consi- 

 derable decrease in number of the green algae and a considerable 

 increase of colourless ones, so, we might say, together with a 

 transition of green algae into colourless ones, we are now able 

 to state, that this transition is not caused by the combined influence 

 of darkness and the feeding milieu in the sponge tissues but that 

 it must be closely related to the life of the sponge ; in other 

 words, we want a living sponge to perform this transition. 



I am going to prove, that the green symbiotic algae of the fresh- 

 water sponges can only pass into the colourless ones by dying. 



I. Analyzing the nature and number of the symbiotic algae in 

 green and colourless Spongillidae (Table 6), one will find the 

 already mentioned (pag. 35) green and colourless algae. But exa- 

 mining these colourless algae more exactly, we see that there exist 

 3 different forms of them : 1. the colourless ones with clearly 

 marked out internal structure (Fig. 35) mentioned on pag. 36 ; 

 this form is the least numerous ; 2. the colourless algae, the internal 

 structure of which is only visible as a shade (Fig. 36) ; this form 

 is somewhat more numerous (1 and 2 together are the group of 

 the „colourless ones with structure"); 3. the colourless ones, the 

 internal structure of which is no more visible at all, but which 

 appear internally either homogeneous (Fig. 37) or somewhat 

 granular, and wich are the most numerous of the 3 forms (the 

 group of the „colourless ones without structure"). But closely 

 examining one can still detect a 4th group , viz. of „vague 

 shades" of colourless algae, in which there is of course neither 

 any internal structure to be seen. All these forms of symbiotic 

 algae generally occur — as mentioned for the green ones and 



