42 EVENINGS AT THE MICEOSCOPE. 



The object of these ciliary wheels is to keep up a 

 constant current in the water. This fluid, as I have 

 said, enters from without, through the upper orifice of 

 the body, and is hurled over the whole surface of the 

 breathing-sac by means of the ciliary waves, parting 

 with its oxygen, as it goes, to the blood, which streams, 

 as we saw, everywhere between the rows of wheels. 

 But the water has another function : it carries particles 

 of organic matter with it, which are suitable for the 

 nourishment of the creature ; these atoms are carried 

 by the currents with the efl'ete water to the bottom of 

 the sac, and are poured into the stomach, where they 

 are digested ; the innutritive remains, together with 

 the waste water, being discharged through the lateral 

 orifice. 



Thus we see how closely connected are the three 

 cardinal processes of circulation, respiration, and di- 

 gestion. 



