THE BIONOMICS OF CONVOLUTA KOSCOFFENSIS. 381 



" symbiosis." According to this hypothesis, the animal draws 

 upon the reserves of the alga, whilst at the same time pro- 

 viding the alga with an environment suitable for renewing 

 the reserves. Direct evidence of such translocation of food 

 material from alga to animal does not exist, and even the 

 experimental and indirect evidence is not satisfactory. Such 

 evidence as we possess is due to Brandt and Geddes. Brandt 

 (1883) experimented with Sagartia and Aiptasia, and 

 found that when all external sources of food were cut off, 

 those anemones that possessed yellow cells retained their 

 shape and size better than anemones depleted of their cells. 

 Geddes (1879 b) found that dark-kept and therefore pre- 

 sumably starch-depleted Convoluta roscoff ensis died in a 

 day or two, but that isolated specimens lived for weeks 

 apparently without ingesting food. Finally, Brandt found 

 free starch in certain Radiolaria, and concluded that it had 

 passed fi-om the yellow cells. 



These experiments and observations do not afford proof of 

 translocation of the algal reserves to the animal tissues, and 

 Famintzin has shown that the evidence points to digestion of 

 the algal cells. He has repeated Brandt's observations, and 

 finds all stages of decolorisation and dissolution of the yellow 

 cells in Radiolaria and Anemones, and of the green cells in 

 Stentor (1889,1891); whilst Beyerinck (1890) has shown 

 the same to be true for Hydra viridis, thus explaiuing, as 

 it seems to us, the presence of irregular decolorised frag- 

 ments seen by Lankester (1882). The relationship of alga 

 and animal is therefore to be regarded not as a mutual 

 exchange of complementary advantages (symbiosis). The 

 evidence so far accumulated shows that the alga is a parasite 

 liable at any time to absorption and digestion. 



We may therefore summarise the work on zooxanthell^e 

 and zoochlorella) by saying that in Hydra, Stentor, and 

 certain anemones these coloured bodies are immigrant alga3 

 or stages of algte which, if they subserve any function 

 in the animal economy, can at present only be considered 

 as an accessory source of food, available not so much by 



