270 THE AMERICAN MONTHLY [Aug. 



end of the body, and at one point in it and above the 

 peristome the funnel-shaped gullet running down into 

 the body and closed below. Locate inside the body the 

 numerous food-vacuoles, and a single contractile vacuole. 

 Study the end of the gullet and note the gathering par- 

 ticles there of food, keep watch and after a time you 

 will see them constricted off and become one of the food- 

 vacuoles. The nivcleus is a curved rod on the side of 

 the body opposite the mouth, it can best be seen after 

 treatment with reagents. Study the stem carefully to 

 locate the spiral thread inside it, it is this wliich by its 

 contraction coils the stem; how does this benefit Vorti- 

 cella ? 



14. Physiology of Vorticella. — Cyclosis or the cir- 

 culation in the protoplasm of Vorticella can often be seen 

 by the motion among the vacuoles ; the constant action 

 of the cilia is another form of motion; the contraction 

 and expansion of the stem and body are also of this 

 class of functions ; a careful series of drawings should 

 be made to show the steps in the process of contraction 

 and expansion. Jar the slide and you will see that the 

 animal responds by a complete responsive shrinkage of 

 the stem and body. This is the function of irritihility, 

 and the jar would be called a stimulus. Can you deter- 

 mine that Vorticella is sensitive to all changes in its sur- 

 roundings? A current of very weak acid will cause it to 

 contract and strong acid will always kill it in the con- 

 tracted condition. The form of stimulus that most com- 

 monly affects V. is contact with other motile animals in 

 its vicinity. Fission takes place in Vorticella, it may 

 take place in either a longitudinal or a transverse plane, 

 different stages of it or the entire process should if pos- 

 sible be observed. In some cases after fission one of the 

 parts unites with another Vorticella and the two fuse to 

 form a single body, conjugation. It seems that this pro- 



