28 STRUCTURAL AND SYSTEMATIC ZOOLOGY 



stance (protoplasm) ; the position and movements of the 

 contractile vacuoles, one near each -end of the body, by 

 means of which the waste water is removed from the 

 body ; the movements of the cilia near the mouth open- 

 ing which produce currents in the water, thus bringing 

 food particles within reach ; the trichocysts, thought to 

 be organs of defense, lying parallel to one another just 

 under the cuticle (their discharge may be produced by 

 running a drop of acetic acid under the cover glass) ; 

 the large nucleus may be seen lying near the center of 

 the body after the application of a drop of acetic methyl 

 green or of methylene blue (Fig. 9). 



Evidence of the possession of nervous properties will 

 be seen in the animal's extreme sensitiveness to contact 

 with foreign bodies, in its selection of food, which con- 

 sists almost entirely of bacteria, in its tendency to 

 collect on the lighter side of the aquarium jar when 

 the latter stands remote from the window. 



Attention should be called to the possible means of 

 dispersal of the animal, to its value as a scavenger, and 

 particularly to the "physiological division of labor" 

 among the various portions of its body, which, though a 

 single cell, has its parts very plainly adapted to perform 

 many different functions. 



Vorticella 



Material. Specimens are usually to be found attached 

 to the sides of the aquarium in which Paramecium has 

 been raised, or to the fragments of hay, jwater plants, 

 etc., therein. Prepare the specimens according to the 

 directions for Amoeba. 



Topics for Study. With the low power study the 

 shape of the animal, consisting of the body portion and 

 the flexible stalk ; the movements of each part, especially 

 the coiling of the stalk ; the position and movements of 



