iv] MODES OF NUTRITION 99 



ones. This is true generally but we must not forget 

 that many of the processes of the animal are also 

 synthetic. 



Now there are few conceivable forms of structure 

 that have not been evolved among animals and plants, 

 and we may assume that there are also few possibilities 

 of nutrition that have not also been evolved. We 

 have to consider, then, what other modes of nutrition 

 besides the purely plant one (holophytic) and the 

 purely animal one (holozoic) exist among marine 

 organisms. There is obviously a combination of the 

 two, and this occurs among some molluscs, some 

 polyzoa, at least one starfish, many coelenterates, 

 including most corals, many worms, possibly in some 

 sponges, and in a great number of protozoa. In all 

 these cases the animal which exhibits the plant-like 

 mode of nutrition is coloured green, and this is due 

 to the presence of chlorophyll the colouring matter 

 of plants, by reason of which they are able to intercept 

 the energy of sunlight and make use of it in the 

 process of photo-synthesis. The best known case 

 of this kind is that of the worm Convoluta, a full 

 account of which is given in the volume Plant- Animals 

 in this series of Manuals. Convoluta is green because 

 of the presence in its tissues of cells containing 

 chlorophyll ; but it does not necessarily begin life as 

 a green animal, for the green cells are the degenerate 

 remains of algae which have infected the tissues of 



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