It is convenient here to show how similar is the mode ofof animals and saprophytes.
Both pour digestive agents through the cell walls on to the food, causing it to dissolve, I.e. digestion is extracellular, the dissolved material then being absorbed into the cells. Both leave a useless residue from food ; saprophytes leave the ’decayed material, ’ animals void fgeces which have never been a part of the animal but which are the insoluble part of decomposed material that has passed through a tube from one end of the animal to the other. Proteins are built up in both cases from simple peptones and amino-acids and not from sugars and nitrates like green plants. Neither can build up cellulose from simpler carbohydrates. Fungal cellulose is an amino compound having a similar formula to that of chitin.