374 F. W. GAMBLE AND FREDERICK KEEBLE. 



be demonstrated by the use of congo red, wliich becomes 

 altered to blue within the gut (PI. 30, fig. 5), and by 

 pressing the animal on litmus-paper. Even a just-hatched 

 Convoluta gives, by the latter method, a very decided acid 

 reaction, plainly visible to the naked eye. The reaction of the 

 gut of larval,adolescent, and adult Convoluta is equally acid. 



We have already stated that mature Convoluta ros- 

 cof fensis contains brown masses, the remains of digested 

 green cells. This mode of nutrition is strikingly similar to 

 a process which is known to occur in lichens. It has 

 long been known that, in certain species, the algal cells of 

 these organisms may be invaded by the hyphge of the fungus. 

 Peirce (1900) regarded the algal cells as at first parasitic on 

 the fungus, and subsequentl}^ the fungus parasitic on the 

 algse. More recently it has been shown (Elenkin, 1901) that 

 in heteromerous lichens the haustoria-like projections of the 

 fungal hypliEe digest the living substance of the greater pro- 

 portion of the green cells. The debris of the digested cells 

 takes the form of brown masses, and the phenomena are 

 interpreted as proving that in such cases endosaprophytism 

 rather than '' symbiosis " expresses the relation between 

 fungus and alga. It is also known that in Hydra viridis 

 the green cells, after a time, fail to resist the disintegrating 

 action of the endoderm cells, become digested, and their 

 remains form brown or reddish matter (Kleinenberg, 1872, 

 p. 6; Beyerinck, 1890). In none of these cases has it been 

 shown that the plastic materials stored in the coloured cells 

 are absorbed by the animal or by the fungoid tissue, though 

 the presumption is strongly in favour of this view. 



If, in the long interval of immaturity during which we 

 know that Convoluta is absorbing food from without, it 

 is also making use of the plastic materials stored in its green 

 cells, this should be capable of proof by placing the animal 

 under such conditions that its external sources of supply are 

 curtailed, and that loss of plastic material can be estimated. 

 This may readily be done by putting Convoluta in a limited 

 quantity of water free from sand, or in a current of clean 



