LESSON XII 



VORTICELLA AND ZOOTHAMNIUM 



The next organism we have to consider is a ciliated infusor 

 even commoner than those described in the two previous 

 lessons. It is hardly possible to examine the water of a 

 pond with any care without finding in it, sometimes attached 

 to weeds, sometimes to the legs of water-fleas, sometimes to 

 the sticks and stones of the bottom, numbers of exquisitely 

 beautiful little creatures, each like an inverted bell with a 

 very long handle, or a wine-glass with a very long stem. 

 These are the well-known " bell-animalcules ; " the com- 

 monest among them belong to various species of the genus 

 Vorticella. 



The first thing that strikes one about Vorticella 

 (Fig. 25, a) is the fact that it is permanently fixed, 

 like a plant, the proximal or near end of the stalk 

 being always firmly fixed to some aquatic object, while to 

 the distal or far end the body proper of the animalcule is 

 attached. 



But in spite of its peculiar form it presents certain very 

 obvious points of resemblance to Paramoecium, Stylonychia, 

 and Opalina. The protoplasm is divided into cortex (Fig. 

 25, c, cori) and medulla (med), and is invested with a 



