INFUSORIAL ANIMALCULES. 57 



polygastric. If solid substances do not exist in the 

 surrounding liquid, then the balls are less solid, and they 

 appear in the forms which they present in the Infusoria 

 plunged in colourless liquids. In this case, the balls are 

 composed of a small number of particles, and principally 

 of a considerable mucous mass, which unites them. 

 Sometimes two balls of this kind are so pressed against 

 each other by the contractions of the animal, that they at 

 last unite. 



" If you wish to follow the formation of these balls, it is 

 necessary to commence these observations at the moment 

 when the Infusoria are plunged into the coloured liquid. 

 The deglutition of the coloured particles takes place very 

 quickly, often in about half a minute, and the coloured 

 balls issue one after another from the stomach, and are 

 pushed downwards along the internal wall of the cavity of 

 the animal. In the genera Paramecium, Kerona, and 

 Vorticella, the new ball pushes the preceding before it, 

 along with the mucosities between them, in such a 

 manner that the first rises along the opposite wall, returns 

 to the other extremity of the cavity, and is pushed down- 

 wards on the other side. The balls thus accumulate in 

 succession till they are expelled one after the other by the 

 anus. The number of these balls is often so consider- 

 able, as to fill the whole cavity of the animals, and so 

 close together, that they form a large mass, which turns 

 slowly upon itself, as among the Vorticella. 



"This rotation is the result of the force with which 

 the newly-formed ball is pushed from the stomach 

 into the cavity, and moves along the under side of the 

 preceding ball. In other cases, where there are not yet 



