138 SYSTEMATIC ZOOLOGY FOR TEACHERS. 



into this. Then the food is ingulfed in a mouth from which it passes into 

 an oesophagus which is provided with small cilia. These cilia cause the food 

 to pass downward into a small chamber or crop. Here, through a whirling 

 motion, also caused by cilia, the food is formed into balls which pass into 

 the protoplasm of the body. Here there is a regular circulation of fluid which 

 carries the balls with it, down one side, across the bottom of the bell and 

 up the other side, following one course indicated by the arrows a s given in 

 fig. 68. By contractions of the central portion of the bell, known as the 

 peristome, the undigested portions of the food are ejected through the vesti- 

 bule. 



Locomotion. Excepting in the male form, explained under reproduction, 

 locomotion in the bell animalcule is confined to contractions of the disk, per- 

 istome and stem. If the dish or slide, containing specimens, be jarred, or the 

 animal touched, it will be seen to first fold in the cilia, then the disk and 

 and a portion of the peristome, while the stem is thrown into a spiral form. 

 All this is done quite rapidly, but in unfolding the motion is much slower. 



Reproduction is by division, from above downward, through the center 

 of each bell, thus the stalk which bore one bell before, bears two after fission. 

 After a short time, one of those bells folds itself as described, acquires a second 

 belt of cilia, breaks off and swims about freely, but soon attaches itself by 

 the base, and forms a new stalk. Before dividing, vorticella undergoes a 

 peculiar process of conjugation. An ordinary bell will either divide rapidly 

 two or more times, thus producing several small individuals, or a small por- 

 tion of a large bell will be divided off. All of these small divisions will 

 produce little bells which swim aboU*t freely, but which soon seek a larger 

 stalked individual, and penetrating into its side, become absorbed by it, thus 

 the identity of the small individual is completely merged into that of the 

 larger. 



Irritability or Nervous System. With a higher degree of speciali- 

 zation, we naturally expect a greater development of nervous irritability and 

 such will doubtless be found to occur in vorticella. 



Encystment. Under some circumstances, vorticella becomes encysted. 

 The cilia, mouth, stalk, and peristone are lost, and the whole animal becomes 

 rounded in form and surrounded by a thick membrane. In this stage, the 

 body is sometimes seen to break up into a number of minute spherical bodies, 

 each of which contains a portion of the nucleus. When liberated by the 

 bursting of the membrane, each of these acquires a ciliated belt, by the aid of 

 which it moves to some favorable spot, becomes attached, loses its belt, and 

 develops a stalk and peristone. 



Summary and Advancement. Although vorticella may, at first sight, 

 be considered as lower in the scale than the slipper infusoria, on account of 

 being attached to a base in its adult stage, the fact that the small, or as we 



