INFUSORIA. 143 



down with it. The Yorticellse are very common, scarce- 

 ly a leaflet of any aquatic plant is without them. They 

 are usually colorless, although green ones do occur. 

 The body is bell-shaped, the narrow part of the bell be- 

 ing fastened to the top of the stem. The front border 

 is surrounded by a circle of fine cilia which need a high 

 power to show them. They produce currents in the 

 water similar to those of Epistylis, and for the same 

 food-collecting purposes. 



The contractions are surprising in their suddenness. 

 While the observer is quietly gazing at the graceful 

 creature whirling its cilia and making tre- 

 mendous whirlpools on a small scale, it dis- 

 appears like a flash, and the student feels 

 like looking for it on the table. But pres- 

 ently it slowly begins to rise from the plant 

 against which it was crouching, and the 

 coiled stem lengthens as it straightens. 

 Yery often it hardly extends before it again leaps out 

 of sight, or close to the object supporting the stem; 

 "When the stem throws itself into spirals, the body of 

 the animal folds together into a ball. 



This will probably be one of the first Infusoria to at- 

 tract the beginner's attention, and he will think it a 

 wonderful thing, as it is. The figure shows some ex- 

 tended and some contracted. They are often found in 

 clusters, sometimes of a hundred or more, all bobbing 

 and swaying in a very curious way, for when one con- 

 tracts it usually sets them all off. 



