1067 



sponge and green alga, considered from the point of view of the 

 advantage to the sponge, is indeed a symbiosis, although by no 

 means so complete as that of the lichens. 



If on the other hand the significance of the oxygen produced b}' 

 the alga is only of subsidiary importance, then, whatever may be the 

 real cause of the death of the algae iii sponge-tissue, whether it be the 

 need of food of the sponge or (and) the "poisoning" of the algae 

 by the products of metabolism of the sponge, in either case we may, 

 indeed we must conclude that, practically speaking, this so called 

 symbiotic relation of sponge and alga is i-eally nothine: but 

 simply a nutrition-process of the sponge, or, if one likes, a very 

 first transition from a nutrition-process into a symbiosis. This holds 

 good in any case for a sponge in the dark. 



For I have established the following : 



The sponge continually imports green algae from the surrounding 

 water into its amoebocytes; here those algae — this should be 

 explicitly staled — are killed and digested by the sponge only for 

 a part, when circumstances are favourable, while the rest can live 

 on, photosynthesise and multiply. (And will give to the sponge- 

 tissue their oxygen formed in light — the only argument that can 

 be brought up in favour of the conception of symbiosis !) This 

 favourable case is only realized in sponges growing in light, and then 

 not even always. When circumstances are however somewhat 

 less favourable — as is the rule with sponges in darkness, and 

 as sometimes also happens when they are in light — then all im- 

 ported algae (and all that might be present already) are continually 

 and unavoidably destroyed and digested by the sponge. 



y. Instead of being considered as a classic example of symbiosis in 

 the sense of the mutualism of the lichens, the association of sponge and 

 alga should therefore be called at most a transition from a nutrition- 

 process (of the sponge) into a still wholly imperfect symbiosis. 



B. The Movement of Water through the Canal System. 



I have discovered a method, which makes it possible to observe 

 for hours loholly intact normally living sponge-tissue with 

 an oil-immersion, on many consecutive days. It was by the aid of 

 these living microscopic preparations that I was able to determine 

 the mode of movement of the flagella of the choanocytes in the 

 flagellated chambers, that is the actual cause of the water- 

 current in the canals, as well as the way in which the food- 

 particles in the sponge are captured and the manner in which defecation 

 and excretion take place (see below). 



