The food must be digested, absorbed and excreted with great rapidity.
The cells which line them and also the cavities of the tubes contain urates, which are excreted from the blood in the surrounding bodycavity.
The protoplasm derives its food from substances in solution in the water; the various waste products which are incident to its life are excreted into it, and so removed from the sphere of its activity.
But it also appears that honeydew may be excreted by ordinary processes of over-turgescence pressing the liquid through water-pores, as in the tropical Caesalpinia, Calliandra, &c. That these exudations on leaves should afterwards serve as pabulum for Fungie.g.
It is excreted when many aromatic compounds, such as benzoic acid and toluene, are taken internally.