NUTRITION OF MARINE ANIMALS 1 59 



waste. When a sponge is fed with readily recognisable 

 substances, such as carmine or milk, and afterwards 

 sectioned, the grains or globules may be found — (a) in the 

 collared flagellate cells ; {b) in the adjacent phagocytes of 

 the mesogloea ; (c) in the phagocytes surrounding the sub- 

 dermal spaces, if these exist. It is uncertain whether the 

 epithelium of the subdermal spaces or the flagellate lining 

 of the deeper cavities is the more important area of absorp- 

 tion, but it is certain that the phagocytes play an important 

 part in engulfing and transporting particles, in digesting 

 those which are useful, and in getting rid of the useless. 

 In extracts of several sponges, Krukenberg and others have 

 found digestive ferments, probably formed within the 

 phagocytes, but digestion is wholly intracellular. 



Many sponges contain much pigment ; thus the lipo- 

 chrome pigment zoonerythrin (familiar in lobsters) is 

 common. Some pigments, such as floridine, may help in 

 respiration. The green pigment of the fresh-water sponge 

 is due to the presence of green symbiotic algae {Chlorella), 

 which in their holophytic activity probably supply food- 

 stuflFs to the host. 



Nutrition of marine animals. — Much discussion has 

 centred round the thesis maintained by Putter, that marine 

 animals find a valuable source of energy in organic com- 

 pounds present in solution in the water. He maintains, 

 for instance, that although a sponge may pass five times 

 its own weight of water through its canals in an hour, yet 

 the particulate, solid food contained in this amount of 

 water is insufficient for the sponge's needs, so that there 

 must be absorption of dissolved food-material. Similar 

 arguments are advanced for higher animals, including 

 fishes, with the corollary assumption that such forms are 

 able to absorb organic substances through their gills 

 or elsewhere. Nearly every fink in Putter's chain of 

 argument has been violently assailed, though it has also 

 found many supporters. It is admitted that sea-water 

 may contain considerable quantities of dissolved organic 

 compounds, but it is uncertain whether any of these 

 are valuable as food-stuffs. The view that there is an 

 insufficiency of solid food is disputed, and unfortunately 

 there has 'been much confusion in the controversy, some 



