348 ANIMAL BIOLOGY. [Part II. 



when it has reached a certain size, it suddenly disappears. The 

 diastole is slow, the systole rapid. When a little finely-divided 

 carmine is mixed with the water in which a vorticella is under 

 observation, the method of feeding may be watched. The fine 

 particles are driven by the cilia into the vestibule, and accumu- 

 late at its blind end. After a while they suddenly burst 

 through into the soft inner substance of the body, carrying with 

 them an equal or even greater amount of water. Thus are 

 formed food-vacuoles, which float freely for a time with a circu- 

 latory motion in the soft protoplasm of the body substance. 

 Such digestible matter as the food may contain is extracted, and 

 the indigestible refuse is passed out into the vestibule through 

 the potential anus. It is probable that the contractile vesicle has 

 the function of draining off" the excess of water thus introduced 

 within the body, in which case it must be regarded as excretory 

 At the same time it is not improbable that the water thus in- 

 troduced within the body, and circulating through its substance, 

 serves also to oxygenate the protoplasm, and thus ministers to a 

 rudimentary respiratory function. 



When a vorticella is disturbed, by a sudden shock given to 

 the stage of the microscope for example, the long stem rapidly 

 coils up like a cork-screw (Fig. 102, B.), and the animal is thus 

 drawn back towards its point of attachment. At the same time 

 the lips of the peristome close in and apply themselves to the 

 disc, which is also retracted. The organism thus becomes pear- 

 shaped. Soon, however, the stalk will uncoil and lengthen out 

 again, the disc will be protruded, the peristome will open out, 

 and the cilia will recommence their orderly vibrations. Nothing 

 can be more beautiful than a colony of vorticellidae alternately 

 contracting and expanding, their stems rapidly coiling and un- 

 coiling. 



The cilia are developed on the ectosarc. Each is a delicate 

 structureless process, which, when the vorticella is in the 

 expanded condition, is in constant motion, alternately bend- 

 ing and straightening. Currents are produced in the water by 

 their continuous motion, and these currents may be readily 

 observed if a little powdered carmine be added to the water 



