128 DROPS OF WATER. 



ture suddenly fall into a drooping posture when 

 danger approaches, as if its minute stalk had a 

 joint near where it is attached to the main stem ; 

 after the lapse of a moment, it again rises, and 

 renews its search for food. E.parasitica is small 

 and solitary. There are several other species. 



The species of the genus Opercularia have a 

 stiff stalk, and much branched ; but the bells, 

 or little bodies, are of different shapes and sizes. 

 The genus ZootJiamnium has a flexible stalk, and 

 the bodies of different forms. Z. arbuscula is much 

 divided, forming objects like beautiful little trees, 

 or plumes of feathers. Most of these curious 

 genera of the family Vorticellina may be seen with 

 ease by the aid of a good microscope, and will 

 amply reward the patient investigator by the 



